GHA: Do not build on 5.5, use checkout v4

... and Xcode latest.

SwiftNIO doesn't seem to build w/ 5.5 anymore?

Author: helje5

.github/workflows/swift.yml

@@ -13,12 +13,11 @@ jobs:
       fail-fast: false
       matrix:
         image:
-          - swift:5.5.0-focal
           - swift:5.10.1-noble
     container: ${{ matrix.image }}
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Build Swift Debug Package
         run: swift build -c debug
       - name: Build Swift Release Package
@@ -29,9 +28,9 @@ jobs:
       - name: Select latest available Xcode
         uses: maxim-lobanov/setup-xcode@v1.2.1
         with:
-          xcode-version: 15.4
+          xcode-version: latest
       - name: Checkout Repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Build Swift Debug Package
         run: swift build -c debug
       - name: Build Swift Release Package