Add external repo tracking for sphinx-exercise and sphinx-proof

Author: mmcky

.github/workflows/weekly-report.yml

@@ -25,6 +25,7 @@ jobs:
           organization: 'QuantEcon'
           output-format: 'markdown'
           exclude-repos: 'lecture-.*\.notebooks,test-.*'
+          track-external-repos: 'executablebooks/sphinx-exercise,executablebooks/sphinx-proof'
 
       - name: Create issue with report
         uses: actions/github-script@v7