Exclude old_topotools.py

Do not want to touch the old topotools file for reference.

.github/workflows/testing.yml

@@ -45,7 +45,7 @@ jobs:
       run: |
         cd geoclaw
         # stop the build if there are Python syntax errors or undefined names
-        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics --exclude old_dtopotools.py
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
         flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
     - name: Test with pytest