Using Swift 6 now for GitHub actions.

.github/workflows/documentation.yml

@@ -25,6 +25,10 @@ jobs:
         uses: actions/checkout@v4
       - name: Setup Pages
         uses: actions/configure-pages@v4
+      - name: Setup Swift
+        uses: swift-actions/setup-swift@v1
+        with:
+          swift-version: "6.0"
       - name: Build documentation
         run: |
           swift package --allow-writing-to-directory ./docs \