Fix spelling

Author: richelbilderbeek

.github/workflows/check_spelling.yaml

@@ -24,6 +24,6 @@ jobs:
           rm -rf docs/old
           rm -rf meeting_notes
           rm $(find . | grep "_old\\.")
-          rm $(find . | grep "not_used")
+          rm $(find . | grep "not_used/[A-Za-z]")
 
       - uses: igsekor/pyspelling-any@v1.0.4