Update GitHub Actions workflow

Author: atdrendel

.github/workflows/ci.yml

@@ -4,11 +4,11 @@ on: push
 
 jobs:
   test:
-    runs-on: macos-12
+    runs-on: macos-15
 
     steps:
-      - uses: actions/checkout@v3
-      - name: Select Xcode 14
-        run: sudo xcode-select -s /Applications/Xcode_14.1.app
+      - uses: actions/checkout@v4
+      - name: Select Xcode 26
+        run: sudo xcode-select -s /Applications/Xcode_26.3.app
       - name: Test
         run: swift test