Simplify and update verify-templating.yml

This makes it print out a diff when there is an error (instead of just a list of files that are wrong), which will make the error more obvious.  I also added `workflow_dispatch` so we can run it manually.

Author: tianon

.github/workflows/verify-templating.yml

@@ -3,8 +3,7 @@ name: Verify Templating
 on:
   pull_request:
   push:
-    branches:
-      - master
+  workflow_dispatch:
 
 defaults:
   run:
@@ -16,9 +15,5 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Apply Templates
-        run: ./apply-templates.sh
-      - name: Check Git Status
-        run: |
-          status="$(git status --short)"
-          [ -z "$status" ]
+      - run: ./apply-templates.sh
+      - run: git diff --exit-code