tests: Fix collection errors when importing tests have side effects

[echoix]

Some test files do some actions, like set up steps outside the set up functions. So, simply importing them for collection, even with pure unittest python -m unittest discover, would have side effects and possibly fail.

With the following change in pyproject.toml for allowing to discover gunittest tests with pytest:

-python_files = "*/tests/*_test.py */tests/test_*.py"
+python_files = """
+    */tests/*_test.py
+    */tests/test_*.py
+    **/testsuite/*test*.py
+"""

These errors are now pointed out.
This PR fixes these collection errors, so at least pytest, if configured correctly to be able to find and import grass from python, doesn't fail anymore.

[echoix]

I read a bit too fast what the lines were doing for one of these test files. They don't actually create the files, only the file names. So, using gs.try_remove instead, as one of them would be created per test, not all of them.

gs.try_remove simply ignores errors if the call fails:

def try_remove(path: StrOrBytesPath) -> None:
    """Attempt to remove a file; no exception is generated if the
    attempt fails.

    :param str path: path to file to remove
    """
    try:
        os.remove(path)
    except Exception:
        pass