ci(dockerized): do show the result of failing tests again

The quality of tests and test suites is most apparent not when
everything passes, but in how quickly bugs can be identified,
analyzed, and resolved after test failures occur.

As such, it is an unfortunate side effect of 2a21098b98 (github: adapt
containerized jobs to be rootless, 2025-01-10) that the output of failed
test cases, which was shown before that change directly in the build
logs, is now no longer shown at all.

The reason is a side effect of trying to run the build and the tests
with permissions other than the `root` user, but without providing the
prerequisite permissions to signal what tests failed and whose output
hence needs to be included in the logs.

The way this signaling works is for the workflow to write into
special-purpose files whose path is specific to the current workflow
step and which can be accessed via the `$GITHUB_ENV` environment
variable, which differs between workflow steps. It is this file that is
missing write permission for the `builder` user that was introduced in
above-mentioned commit.

The solution is simple: make the file world-writable.

Technically, this write permission should be removed after the step has
completed, if proper security practices were to be upheld, but since
nothing uses that file again, it does not matter, and the fix is more
succinct this way.

This commit is best viewed with `--color-words`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
[jc: squashed Elijah's rewrite of the first paragraph of the log message]
[jc: updated chmod to match "world-writable" in the log message]
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.github/workflows/main.yml

@@ -417,7 +417,7 @@ jobs:
     - run: ci/install-dependencies.sh
     - run: useradd builder --create-home
     - run: chown -R builder .
-    - run: sudo --preserve-env --set-home --user=builder ci/run-build-and-tests.sh
+    - run: chmod a+w $GITHUB_ENV && sudo --preserve-env --set-home --user=builder ci/run-build-and-tests.sh
     - name: print test failures
       if: failure() && env.FAILED_TEST_ARTIFACTS != ''
       run: sudo --preserve-env --set-home --user=builder ci/print-test-failures.sh