Add cross-platform compatibility for the new exec type post_write_hook by changing executable to a list

[caffeinatedMike]

I'm trying to utilize ruff in my post_write_hooks section of alembic.ini by using the new exec type hook introduced by #1275 and released in #1276. With this new hook type I'm running into an issue when developing on different platforms (Windows and Linux). When pip installing packages on windows all executables (like ruff) are placed in .venv/Scripts/*, while Linux places them in .venv/bin/*.

What I think would be beneficial is to introduce a change to the hook.executeable field that makes it a list instead of a singular value. Then, when the hook runs it would try to locate the executable in the first location and move onto the next location if the executable was not found. That would allow cross-platform functionality without needing to modify the alembic.ini file whenever pulling down a repository or needing to maintain two different versions for different platforms.

[post_write_hooks]
hooks = ruff
# lint with attempts to fix using "ruff" - use the exec runner, execute a binary
ruff.type = exec
ruff.executable = %(here)s/.venv/bin/ruff, %(here)s/.venv/Scripts/ruff
ruff.options = --fix REVISION_SCRIPT_FILENAME