Add required PR Check action (#249)

Our PR jobs now call into templates and use a matrix strategy for all
tested configurations.

GitHub Actions branch protections do not let you set "all jobs are
required" nor even "all matrix permutations of this one job" are
required.

You literally have to set every individual permutation as required
manually, which makes it hard to maintain.

This PR adds a final "Successful PR Check" job that is dependent on all
the others, that can be the *one* set to required.

.github/workflows/pr.yml

@@ -84,3 +84,10 @@ jobs:
       vmImage: windows-2022
       configuration: ${{ matrix.configuration }}
       platform: ${{ matrix.platform }}
+
+  prcheck:
+    name: Successful PR Check
+    runs-on: ubuntu-latest
+    needs: [setupcheck, call-runcodegen, call-testcli, call-testcli-old, call-buildnpmpackage, call-buildrnx]
+    steps:
+     - uses: actions/checkout@v3