Change Node.reportinfo() return value from py.path to str|os.PathLike[str]

`reportinfo()` is the last remaining py.path-only code path in pytest,
i.e. the last piece holding back py.path deprecation. The problem with
it is that plugins/users use it from both sides -- implementing it
(returning the value) and using it (using the return value). Dealing
with implementers is easy enough -- allow to return `os.PathLike[str]`.
But for callers who expect strictly `py.path` this will break and
there's not really a good way to provide backward compat for this.

From analyzing a corpus of 680 pytest plugins, the vast majority of
`reportinfo` appearances are implementations, and the few callers don't
actually access the path part of the return tuple.

As for test suites that might access `reportinfo` (e.g. using
`request.node.reportinfo()` or other ways), that is much harder to
survey, but from the ones I searched, I only found case
(`pytest_teamcity`, but even then it uses `str(fspath)` so is unlikely
to be affected in practice). They are better served with using
`node.location` or `node.path` directly.

Therefore, just break it and change the return type to
`str|os.PathLike[str]`.

Refs #7259.

doc/en/example/nonpython/conftest.py

@@ -40,7 +40,7 @@ class YamlItem(pytest.Item):
             )
 
     def reportinfo(self):
-        return self.fspath, 0, f"usecase: {self.name}"
+        return self.path, 0, f"usecase: {self.name}"
 
 
 class YamlException(Exception):