GitHub Actions: cpplint and clang-format checks on PRs only

With 2964edf various checks are now also being run after the
merge into develop (so as to make sure that GitHub's cache is adequately
populated). The syntactic checks of the PR-specific diff neither work
nor make sense upon push. This commit moves them into a YAML file of
their own and limits their execution to pull requests only. No code
changes.

Author: tautschnig

.github/workflows/pull-request-checks.yaml

@@ -593,50 +593,6 @@ jobs:
       - name: Run CBMC regression tests
         run: make CXX=clcache BUILD_ENV=MSVC -C regression test
 
-  # This job takes approximately 1 minute
-  check-clang-format:
-    runs-on: ubuntu-20.04
-    steps:
-      - uses: actions/checkout@v3
-        with:
-          submodules: recursive
-          fetch-depth: 0
-      - name: Fetch dependencies
-        env:
-          # This is needed in addition to -yq to prevent apt-get from asking for
-          # user input
-          DEBIAN_FRONTEND: noninteractive
-        run: |
-          sudo apt-get update
-          sudo apt-get install --no-install-recommends -yq clang-format-11
-      - name: Check updated lines of code match clang-format-11 style
-        env:
-          BASE_BRANCH: ${{ github.base_ref }}
-          MERGE_BRANCH: ${{ github.ref }}
-        run: ./.github/workflows/pull-request-check-clang-format.sh
-
-  # This job takes approximately 1 minute
-  check-cpplint:
-    runs-on: ubuntu-20.04
-    steps:
-      - uses: actions/checkout@v3
-        with:
-          submodules: recursive
-          fetch-depth: 0
-      - name: Fetch dependencies
-        env:
-          # This is needed in addition to -yq to prevent apt-get from asking for
-          # user input
-          DEBIAN_FRONTEND: noninteractive
-        run: |
-          sudo apt-get update
-          sudo apt-get install --no-install-recommends -yq python3-unidiff
-      - name: Check updated lines of code meet linting standards
-        env:
-          BASE_BRANCH: ${{ github.base_ref }}
-          MERGE_BRANCH: ${{ github.ref }}
-        run: ./.github/workflows/pull-request-check-cpplint.sh
-
   # This job takes approximately 32 minutes
   windows-msi-package:
     runs-on: windows-2019

.github/workflows/syntax-checks.yaml

@@ -0,0 +1,49 @@
+name: Syntactic checks
+on:
+  pull_request:
+    branches: [ develop ]
+
+jobs:
+  # This job takes approximately 1 minute
+  check-clang-format:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          submodules: recursive
+          fetch-depth: 0
+      - name: Fetch dependencies
+        env:
+          # This is needed in addition to -yq to prevent apt-get from asking for
+          # user input
+          DEBIAN_FRONTEND: noninteractive
+        run: |
+          sudo apt-get update
+          sudo apt-get install --no-install-recommends -yq clang-format-11
+      - name: Check updated lines of code match clang-format-11 style
+        env:
+          BASE_BRANCH: ${{ github.base_ref }}
+          MERGE_BRANCH: ${{ github.ref }}
+        run: ./.github/workflows/pull-request-check-clang-format.sh
+
+  # This job takes approximately 1 minute
+  check-cpplint:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          submodules: recursive
+          fetch-depth: 0
+      - name: Fetch dependencies
+        env:
+          # This is needed in addition to -yq to prevent apt-get from asking for
+          # user input
+          DEBIAN_FRONTEND: noninteractive
+        run: |
+          sudo apt-get update
+          sudo apt-get install --no-install-recommends -yq python3-unidiff
+      - name: Check updated lines of code meet linting standards
+        env:
+          BASE_BRANCH: ${{ github.base_ref }}
+          MERGE_BRANCH: ${{ github.ref }}
+        run: ./.github/workflows/pull-request-check-cpplint.sh