config: Handle NotADirectoryError exception in exists_accessible

Make the function returns False when such exception is raised,
for instance when a .swh file exists in home directory.

It fixes pre-commit mypy check in swh-web for such edge cases.

swh/core/config.py

@@ -62,7 +62,7 @@ def exists_accessible(filepath: str) -> bool:
         os.stat(filepath)
     except PermissionError:
         raise
-    except FileNotFoundError:
+    except (FileNotFoundError, NotADirectoryError):
         return False
     else:
         if os.access(filepath, os.R_OK):