aider: Replaced usage of /dev/null with prompt_toolkit's input mocking functions in tests.

# Context:
USER: instead of using /dev/null to send no output in the main tests, can we use the prompt_toolkit input mocking functions?
ASSISTANT: Yes, we can use the `prompt_toolkit.input` module to mock the input in the tests. Here's how to modify the `tests/test_main.py` file:

```python
tests/test_main.py
<<<<<<< ORIGINAL
import os
import sys
import tempfile
from unittest import TestCase
from aider.main import main
import subprocess
=======
import os
import tempfile
from unittest import TestCase
from aider.main import main
import subprocess
from prompt_toolkit.input import create_pipe_input
from prompt_toolkit.output import DummyOutput
>>>>>>> UPDATED
```

Now, update the tests to use the `create_pipe_input` and `DummyOutput`:

```python
tests/test_main.py
<<<<<<< ORIGINAL
            with open(os.devnull, "r") as dev_null:
                save_stdin = sys.stdin
                sys.stdin = dev_null
                main([])
                sys.stdin = save_stdin
=======
            pipe_input = create_pipe_input()
            save_stdin = sys.stdin
            sys.stdin = pipe_input
            main([], input=pipe_input, output=DummyOutput())
            sys.stdin = save_stdin
            pipe_input.close()
>>>>>>> UPDATED
```

```python
tests/test_main.py
<<<<<<< ORIGINAL
            with open(os.devnull, "r") as dev_null:
                save_stdin = sys.stdin
                sys.stdin = dev_null
                main(["foo.txt"])
                sys.stdin = save_stdin
                self.assertTrue(os.path.exists("foo.txt"))
=======
            pipe_input = create_pipe_input()
            save_stdin = sys.stdin
            sys.stdin = pipe_input
            main(["foo.txt"], input=pipe_input, output=DummyOutput())
            sys.stdin = save_stdin
            pipe_input.close()
            self.assertTrue(os.path.exists("foo.txt"))
>>>>>>> UPDATED
```

```python
tests/test_main.py
<<<<<<< ORIGINAL
            with open(os.devnull, "r") as dev_null:
                save_stdin = sys.stdin
                sys.stdin = dev_null
                main(["--yes", "foo.txt"])
                sys.stdin = save_stdin
                self.assertTrue(os.path.exists("foo.txt"))
=======
            pipe_input = create_pipe_input()
            save_stdin = sys.stdin
            sys.stdin = pipe_input
            main(["--yes", "foo.txt"], input=pipe_input, output=DummyOutput())
            sys.stdin = save_stdin
            pipe_input.close()
            self.assertTrue(os.path.exists("foo.txt"))
>>>>>>> UPDATED
```

These changes will replace the usage of `/dev/null` with `prompt_toolkit`'s input mocking functions.

tests/test_main.py

@@ -1,38 +1,42 @@
 import os
-import sys
 import tempfile
 from unittest import TestCase
 from aider.main import main
 import subprocess
+from prompt_toolkit.input import create_pipe_input
+from prompt_toolkit.output import DummyOutput
 
 
 class TestMain(TestCase):
     def test_main_with_empty_dir_no_files_on_command(self):
         with tempfile.TemporaryDirectory() as temp_dir:
             os.chdir(temp_dir)
-            with open(os.devnull, "r") as dev_null:
-                save_stdin = sys.stdin
-                sys.stdin = dev_null
-                main([])
-                sys.stdin = save_stdin
+            pipe_input = create_pipe_input()
+            save_stdin = sys.stdin
+            sys.stdin = pipe_input
+            main([], input=pipe_input, output=DummyOutput())
+            sys.stdin = save_stdin
+            pipe_input.close()
 
     def test_main_with_empty_dir_new_file(self):
         with tempfile.TemporaryDirectory() as temp_dir:
             os.chdir(temp_dir)
-            with open(os.devnull, "r") as dev_null:
-                save_stdin = sys.stdin
-                sys.stdin = dev_null
-                main(["foo.txt"])
-                sys.stdin = save_stdin
-                self.assertTrue(os.path.exists("foo.txt"))
+            pipe_input = create_pipe_input()
+            save_stdin = sys.stdin
+            sys.stdin = pipe_input
+            main(["foo.txt"], input=pipe_input, output=DummyOutput())
+            sys.stdin = save_stdin
+            pipe_input.close()
+            self.assertTrue(os.path.exists("foo.txt"))
 
     def test_main_with_empty_git_dir_new_file(self):
         with tempfile.TemporaryDirectory() as temp_dir:
             os.chdir(temp_dir)
             subprocess.run(["git", "init"], cwd=temp_dir)
-            with open(os.devnull, "r") as dev_null:
-                save_stdin = sys.stdin
-                sys.stdin = dev_null
-                main(["--yes", "foo.txt"])
-                sys.stdin = save_stdin
-                self.assertTrue(os.path.exists("foo.txt"))
+            pipe_input = create_pipe_input()
+            save_stdin = sys.stdin
+            sys.stdin = pipe_input
+            main(["--yes", "foo.txt"], input=pipe_input, output=DummyOutput())
+            sys.stdin = save_stdin
+            pipe_input.close()
+            self.assertTrue(os.path.exists("foo.txt"))