CI: Enforce status checks once pull requests received (#113)

We tend to reject the pull requests if they fail to pass coding style checks
and static analysis.

See https://www.wesleyhaakman.org/working-with-pull-requests-status-checks-arm-templates-and-github-actions/

.github/workflows/generate_doc.yaml

@@ -35,17 +35,3 @@ jobs:
             lkmpg-html.tar.gz
           tag_name: "latest"
           prerelease: true
-
-  validate:
-    runs-on: ubuntu-20.04
-    steps:
-      - name: checkout code
-        uses: actions/checkout@v2
-      - name: validate coding style and functionality
-        run: |
-            sudo apt-get install -q -y clang-format-11
-            sudo apt-get install -q -y cppcheck
-            .ci/check-format.sh
-            .ci/static-analysis.sh
-            .ci/build-n-run.sh
-        shell: bash

.github/workflows/status-check.yaml

@@ -0,0 +1,24 @@
+name: status-checks
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+  workflow_dispatch:
+
+jobs:
+  validate:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: checkout code
+        uses: actions/checkout@v2
+      - name: validate coding style and functionality
+        run: |
+            sudo apt-get install -q -y clang-format-11
+            sudo apt-get install -q -y cppcheck
+            .ci/check-format.sh
+            .ci/static-analysis.sh
+            .ci/build-n-run.sh
+        shell: bash