Update deploy_site.yml

attempting to fix #729

Author: ahouseholder

.github/workflows/deploy_site.yml

@@ -49,6 +49,7 @@ jobs:
 
       - name: Build Site
         run: |
+          export PYTHONPATH=./src;$PYTHONPATH
           mkdocs build --verbose --clean --config-file mkdocs.yml       
 
       - name: Upload artifact