cache defeats flake8-executable

[dimbleby]

$ ruff .
foo.py::1:3: EXE001 Shebang is present but file is not executable
Found 1 error.

$ chmod +x foo.py

$ ruff .
foo.py::1:3: EXE001 Shebang is present but file is not executable
Found 1 error.

Need to clear the ruff cache to get it to notice that this is fixed.

[charliermarsh]

We need to use ctime on Unix platforms.