Simplify validate workflow (use regex)

Author: stancl

.github/workflows/validate.yml

@@ -8,14 +8,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - name: Check for todo0
-      run: '! grep -r "todo0" --exclude-dir=workflows .'
-      if: always()
-    - name: Check for todo1
-      run: '! grep -r "todo1" --exclude-dir=workflows .'
-      if: always()
-    - name: Check for todo2
-      run: '! grep -r "todo2" --exclude-dir=workflows .'
+    - name: Check for priority todos
+      run: '! grep -r "todo[0-9]" --exclude-dir=workflows .'
       if: always()
     - name: Check for non-todo skip()s in tests
       run: '! grep -r "skip(" --exclude-dir=workflows tests/ | grep -v "todo"'