chore: add protos check action (#267)

**Description**

Adding a generated-protos check action on any branch push to check
protos as minor bumps from deps updates can introduce formatting changes
if local tools are slightly out of sync.

This is useful to run prior to release actions.

Author: matthewmcneely

.github/workflows/ci-pydgraph-tests.yml

@@ -3,15 +3,15 @@ name: ci-pydgraph-tests
 on:
   push:
     branches:
-      - master
+      - main
   pull_request:
     types:
       - opened
       - reopened
       - synchronize
       - ready_for_review
     branches:
-      - master
+      - main
   schedule:
     - cron: 1 0 * * * # run workflow daily
 
@@ -54,5 +54,10 @@ jobs:
           cd pydgraph
           python -m pip install --upgrade pip
           python -m pip install .[dev]
+      - name: Verify that updated protobufs are checked in
+        run: |
+          cd pydgraph
+          python scripts/protogen.py
+          git diff --exit-code -- .
       - name: Run tests
         run: cd pydgraph && DGRAPH_IMAGE_TAG=local bash scripts/local-test.sh