Catch OSError from getpass.getuser() (#11875)

- Previously, `getpass.getuser()` would leak an ImportError if the
  USERNAME environment variable was not set on Windows because the `pwd`
  module cannot be imported.
- Starting in Python 3.13.0a3, it only raises `OSError`.

Fixes #11874

AUTHORS

@@ -340,6 +340,7 @@ Ronny Pfannschmidt
 Ross Lawley
 Ruaridh Williamson
 Russel Winder
+Russell Martin
 Ryan Puddephatt
 Ryan Wooden
 Sadra Barikbin

changelog/11875.bugfix.rst

@@ -0,0 +1 @@
+Correctly handle errors from :func:`getpass.getuser` in Python 3.13.

src/_pytest/tmpdir.py

@@ -204,7 +204,7 @@ def get_user() -> Optional[str]:
         import getpass
 
         return getpass.getuser()
-    except (ImportError, KeyError):
+    except (ImportError, OSError, KeyError):
         return None