Revert "py(pyproject[ruff]): Ignore shell.py importlib nits"

This reverts commit a39392a.

Author: tony

pyproject.toml

@@ -172,10 +172,6 @@ convention = "numpy"
 "src/tmuxp/workspace/finders.py" = ["PTH"]
 "src/tmuxp/cli/*.py" = ["PTH"]
 "docs/_ext/aafig.py" = ["PTH"]
-"src/tmuxp/shell.py" = [
-  "F401",   # Consider using `importlib.util.find_spec` to test for availability
-  "RUF100"  # Unused `noqa` directive (unused: `F841`)
-]
 
 [tool.pytest.ini_options]
 addopts = "--reruns=0 --tb=short --no-header --showlocals --doctest-modules"