Add CodeQL (#188)

Add GitHub Actions workflow to run CodeQL for GitHub Actions and C#.

Author: martincostello

.github/workflows/codeql.yml

@@ -0,0 +1,67 @@
+name: codeql
+
+on:
+  push:
+    branches: [ main ]
+    paths-ignore:
+      - '**.md'
+  pull_request:
+    branches: [ main ]
+  schedule:
+    - cron: '0 6 * * MON'
+  workflow_dispatch:
+
+permissions: {}
+
+jobs:
+  analysis:
+    runs-on: ubuntu-latest
+
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [ 'actions', 'csharp' ]
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      with:
+        filter: 'tree:0'
+        persist-credentials: false
+        show-progress: false
+
+    - name: Initialize CodeQL
+      uses: github/codeql-action/init@181d5eefc20863364f96762470ba6f862bdef56b # v3.29.2
+      with:
+        build-mode: none
+        languages: ${{ matrix.language }}
+        queries: security-and-quality
+
+    - name: Perform CodeQL Analysis
+      uses: github/codeql-action/analyze@181d5eefc20863364f96762470ba6f862bdef56b # v3.29.2
+      with:
+        category: '/language:${{ matrix.language }}'
+
+  codeql:
+    if: ${{ !cancelled() }}
+    needs: [ analysis ]
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Report status
+      shell: bash
+      env:
+        SCAN_SUCCESS: ${{ !contains(needs.*.result, 'failure') && !contains(needs.*.result, 'cancelled') }}
+      run: |
+        if [ "${SCAN_SUCCESS}" == "true" ]
+        then
+          echo 'CodeQL analysis successful ✅'
+        else
+          echo 'CodeQL analysis failed ❌'
+          exit 1
+        fi