Add the crazy-max/ghaction-github-status GitHub action

This action is added in a separate "diagnostics" job.  As configured
it will never fail, but it will print out the status of the various
GitHub components.  This information will sometimes be useful when
determining why builds fail after the fact.

.github/workflows/build.yml

@@ -14,6 +14,12 @@ env:
   RUN_TMATE: ${{ secrets.RUN_TMATE }}
 
 jobs:
+  diagnostics:
+    runs-on: ubuntu-latest
+    steps:
+      - id: github-status
+        name: Check GitHub status
+        uses: crazy-max/ghaction-github-status@v3
   lint:
     runs-on: ubuntu-latest
     steps: