[self tests] test_codemod_formatter_error_input fails with black 25.9.0

[stanislavlevin]

test_codemod_formatter_error_input fails with black 25.9.0:

FAIL: test_codemod_formatter_error_input (codemod.tests.test_codemod_cli.TestCodemodCLI.test_codemod_formatter_error_input)
----------------------------------------------------------------------           
Traceback (most recent call last):                                                  
  File "/usr/src/RPM/BUILD/python3-module-libcst-1.8.5/libcst/codemod/tests/test_codemod_cli.py", line 39, in test_codemod_formatter_error_input
    self.assertIn(                                                               
    ~~~~~~~~~~~~~^                                                               
        "error: cannot format -: Cannot parse for target version Python 3.6: 13:10:     async with AsyncExitStack() as stack:",
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        rlt.stderr.decode("utf-8"),                                              
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^                                              
    )                                                                            
    ^                                                                            
AssertionError: 'error: cannot format -: Cannot parse for target version Python 3.6: 13:10:     async with AsyncExitStack() as stack:' not found in 'Calculating full-repo metadata...\nExecuting codemod...\nAll done! ✨ 🍰 ✨\n1 file left unchanged.\n\r\x1b[2K0.28s 0% complete, [calculating] estimated for 1 files to go...\r\x1b[2KFinished codemodding 1 files!\n - Transformed 1 files successfully.\n - Skipped 0 files.\n - Failed to codemod 0 files.\n - 0 warnings were generated.\n'

This test checks the error message in case of source having syntax error.
But https://black.readthedocs.io/en/stable/faq.html#why-does-black-not-detect-syntax-errors-in-my-code

Black is an autoformatter, not a Python linter or interpreter. Detecting
all syntax errors is not a goal. It can format all code accepted by
CPython (if you find an example where that doesn’t hold, please report a
bug!), but it may also format some code that CPython doesn’t accept.

With black < 25.9.0:

$ black --check -t py36 ./lib/python3/site-packages/libcst/codemod/tests/codemod_formatter_error_input.py.txt
error: cannot format lib/python3/site-packages/libcst/codemod/tests/codemod_formatter_error_input.py.txt: Cannot parse for target version Python 3.6: 13:10:     async with AsyncExitStack() as stack:
                                                                                 
Oh no! 💥 💔 💥                                                                  
1 file would fail to reformat.                                                   

black 25.9.0:

$ black --check -t py36 ./lib/python3/site-packages/libcst/codemod/tests/codemod_formatter_error_input.py.txt
All done! ✨ 🍰 ✨                                                                  
1 file would be left unchanged.