add workflow to test for uncommited schema changes (#7467)

This adds a new workflow to CI in order to test that the PR doesn't contain uncommited schema changes, which are the source of many merge conflicts and developer frustration.

.github/workflows/test-schema-changes.yml

@@ -0,0 +1,43 @@
+name: Schema Change Tests
+
+on:
+  push:
+    branches:
+      - main
+      - patch-*
+  pull_request:
+    paths:
+      - 'server/datastore/mysql/schema.sql'
+      - 'server/datastore/mysql/migrations/**.go'
+      - '.github/workflows/test-schema-changes.yml'
+  workflow_dispatch: # Manual
+
+permissions:
+  contents: read
+
+jobs:
+  test-schema-changes:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Install Go
+      uses: actions/setup-go@84cbf8094393cdc5fe1fe1671ff2647332956b1a # v2
+      with:
+        go-version: '^1.17.8'
+    - name: Checkout Code
+      uses: actions/checkout@629c2de402a417ea7690ca6ce3f33229e27606a5 # v2
+
+    - name: Start Infra Dependencies
+      # Use & to background this
+      run: docker-compose up -d mysql_test &
+
+    - name: Dump test schema
+      run: make dump-test-schema
+
+    - name: Verify changes
+      run: |
+        if [[ $(git diff server/datastore/mysql/schema.sql) ]]; then
+          echo "❌ fail: uncommited changes in schema.sql"
+          echo "please run make dump-test-schema and commit the changes"
+          exit 1
+        fi
+