Fix typo in doc with syspath_prepend

src/_pytest/monkeypatch.py

@@ -262,7 +262,7 @@ class MonkeyPatch:
         # A call to syspathinsert() usually means that the caller wants to
         # import some dynamically created files, thus with python3 we
         # invalidate its import caches.
-        # This is especially important when any namespace package is in used,
+        # This is especially important when any namespace package is in use,
         # since then the mtime based FileFinder cache (that gets created in
         # this case already) gets not invalidated when writing the new files
         # quickly afterwards.