Update Tools/check-c-api-docs/main.py

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: ZeroIntensity

Tools/check-c-api-docs/main.py

@@ -28,7 +28,7 @@
 """
 
 
-def found_undocumented(singular: bool):
+def found_undocumented(singular: bool) -> str:
     some = "an" if singular else "some"
     s = "" if singular else "s"
     these = "this" if singular else "these"