chore(migrations): Tidy up generate migration step (#77244)

<!-- Describe your PR here. -->

.github/workflows/migrations.yml

@@ -68,7 +68,7 @@ jobs:
         id: file
         run: |
           echo 'added<<EOF' >> "$GITHUB_OUTPUT"
-          git diff --diff-filter=A --name-only origin/master HEAD -- 'src/sentry/*/migrations/*' 'src/sentry/migrations/*' | grep -v "__init__.py" >> "$GITHUB_OUTPUT"
+          git diff --diff-filter=A --name-only origin/master HEAD -- 'src/sentry/*/migrations/*' 'src/sentry/migrations/*' ':!*/__init__.py' >> "$GITHUB_OUTPUT"
           echo 'EOF' >> "$GITHUB_OUTPUT"
 
       - name: Generate SQL for migration