Add workflow to prevent merging a PR when the NO-MERGE label is app…

…lied (dotnet#111940)

* Add workflow to prevent merging a PR when the `NO-MERGE` label is applied.
* Fix backtick bug in check-service-labels echo too.

.github/workflows/check-no-merge-label.yml

@@ -0,0 +1,25 @@
+name: check-no-merge-label
+
+permissions:
+  pull-requests: read
+
+on:
+  pull_request:
+    types: [opened, edited, reopened, labeled, unlabeled, synchronize]
+    branches:
+      - 'main'
+      - 'release/**'
+
+jobs:
+  check-labels:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check 'NO-MERGE' label
+      run: |
+        echo "Merging permission is disabled when the 'NO-MERGE' label is applied."
+        if [ "${{ contains(github.event.pull_request.labels.*.name, 'NO-MERGE') }}" = "false" ]; then
+          exit 0
+        else
+          echo "::error:: The 'NO-MERGE' label was applied to the PR. Merging is disabled."
+          exit 1
+        fi

.github/workflows/check-service-labels.yml

@@ -15,7 +15,7 @@ jobs:
     steps:
     - name: Check 'Servicing-approved' label
       run: |
-        echo "Merging permission is enabled for servicing PRs when the `Servicing-approved` label is applied."
+        echo "Merging permission is enabled for servicing PRs when the 'Servicing-approved' label is applied."
         if [ "${{ contains(github.event.pull_request.labels.*.name, 'Servicing-approved') }}" = "true" ]; then
           exit 0
         else