patch 9.1.1974: tests: missing cleanup in Test_bwipe_during_save()

Problem:  tests: missing cleanup in Test_bwipe_during_save().
Solution: Reset &charconvert.

closes: #18908

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_buffer.vim

@@ -230,6 +230,7 @@ func Test_bwipe_during_save()
   set charconvert=execute('%bw!')
   call assert_fails('write ++enc=lmao boom', 'E937:')
 
+  set charconvert&
   %bwipe
 endfunc
 

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1974,
 /**/
     1973,
 /**/