Add CodeQL workflow

.github/workflows/codeql.yml

@@ -0,0 +1,50 @@
+name: "CodeQL"
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+  schedule:
+    - cron: "42 4 * * 0"
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: "macos-latest"
+    timeout-minutes: 120
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      # Initializes the CodeQL tools for scanning.
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v2
+        with:
+          languages: swift
+          # If you wish to specify custom queries, you can do so here or in a config file.
+          # By default, queries listed here will override any specified in a config file.
+          # Prefix the list here with "+" to use these queries and those in the config file.
+
+          # For more details on CodeQL's query packs, refer to: https://docs.github.com/en/code-security/code-scanning/automatically-scanning-your-code-for-vulnerabilities-and-errors/configuring-code-scanning#using-queries-in-ql-packs
+          # queries: security-extended,security-and-quality
+
+      - uses: actions/cache@v3
+        with:
+          path: .build
+          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
+          restore-keys: |
+            ${{ runner.os }}-spm-
+
+      - name: Build
+        run: swift build -v
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v2
+        with:
+          category: "/language:swift"