Update CI workflow configuration

The updated configuration includes:
 - Bumped actions/checkout to the latest version.
 - Bumped Xcode version to 26.4.

Author: mgutski

.github/workflows/ci.yml

@@ -28,30 +28,30 @@ concurrency:
 jobs:
   lint:
     name: Lint
-    runs-on: macos-15
+    runs-on: macos-26
 
     steps:
       - name: Install SwiftLint
         run: brew install swiftlint
 
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Lint Swift Code
         run: swiftlint lint --strict --reporter github-actions-logging
 
   dependencies:
     name: Dependencies
-    runs-on: macos-15
+    runs-on: macos-26
     env:
-      DEVELOPER_DIR: "/Applications/Xcode_26.1.app/Contents/Developer"
+      DEVELOPER_DIR: "/Applications/Xcode_26.4.app/Contents/Developer"
 
     steps:
       - name: Runner Overview
         run: system_profiler SPHardwareDataType SPSoftwareDataType SPDeveloperToolsDataType
 
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Resolve Package Dependencies
         run: swift package resolve -v