CI: Bump test.yml Swift version to match package Swift version

Author: stackotter

.github/workflows/test.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Setup Swift
         uses: SwiftyLab/setup-swift@latest
         with:
-          swift-version: "5.7"
+          swift-version: "5.9"
       - name: Checkout
         uses: actions/checkout@v6
       - name: Test