CI: use macos-13 runner

The job was using 'macos-12' runner, which has been
deprecated. Its usage caused error and tests were
not executed.

This commit updates the workflow to use macos-13 image.

Signed-off-by: Patryk Wrobel <183546751+pwrobeldev@users.noreply.github.com>

.github/workflows/functional-tests.yml

@@ -188,7 +188,7 @@ jobs:
 
   swift-mac:
     name: Swift on MacOS
-    runs-on: macos-12
+    runs-on: macos-13
 
     steps:
       - uses: actions/checkout@v2