gh-142315: Add test capturing missed expectation.

[jaraco]

• Issue: Pdb doesn't handle anonymous pipe symlinks #142315

[jaraco]

The test is failing nicely, on Ubuntu only.

ERROR: test_script_target_anonymous_pipe (test.test_pdb.PdbTestCase.test_script_target_anonymous_pipe)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/test_pdb.py", line 3681, in test_script_target_anonymous_pipe
    target = pdb._ScriptTarget(pipe_path)
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/pdb.py", line 190, in __init__
    sys.exit(1)
    ~~~~~~~~^^^
SystemExit: 1

----------------------------------------------------------------------
Ran 1 test in 0.006s

FAILED (errors=1)
test test_pdb failed

[jaraco]

Closing, as we'll merge this failing test with the PR.