Allow Path in polib.pofile()

[m-aciek]

Previously:

% mypy generate.py
translators.py:21: error: No overload variant of "pofile" matches argument type "Path"  [call-overload]
translators.py:21: note: Possible overload variants:
translators.py:21: note:     def [_TP: POFile] pofile(pofile: str, *, klass: type[_TP], **kwargs: Any) -> _TP
translators.py:21: note:     def pofile(pofile: str, **kwargs: Any) -> POFile

Confirmed locally that the changes fixes that.

pofile() uses os.open(), so it works nicely with a Path input.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

schemathesis (https://github.com/schemathesis/schemathesis)
-   File "/tmp/mypy_primer/old_mypy/venv/bin/mypy", line 8, in <module>
+   File "/tmp/mypy_primer/new_mypy/venv/bin/mypy", line 8, in <module>
-   File "/tmp/mypy_primer/old_mypy/venv/lib/python3.13/site-packages/mypy/__main__.py", line 15, in console_entry
+   File "/tmp/mypy_primer/new_mypy/venv/lib/python3.13/site-packages/mypy/__main__.py", line 15, in console_entry

[srittau]

Thanks!