Update CI workflow configuration

Includes:
 - Bumped the jobs runner image to `macos-15`.
 - Bumped Xcode version to 16.4.

Author: mgutski

.github/workflows/ci.yml

@@ -28,7 +28,7 @@ concurrency:
 jobs:
   lint:
     name: Lint
-    runs-on: macos-14
+    runs-on: macos-15
 
     steps:
       - name: Install SwiftLint
@@ -42,9 +42,9 @@ jobs:
 
   dependencies:
     name: Dependencies
-    runs-on: macos-14
+    runs-on: macos-15
     env:
-      DEVELOPER_DIR: "/Applications/Xcode_16.2.app/Contents/Developer"
+      DEVELOPER_DIR: "/Applications/Xcode_16.4.app/Contents/Developer"
 
     steps:
       - name: Runner Overview