[nrf fromtree] github: hello_world_multiplatform: retire macos-13

This runner is going to go away soon, drop it.

Link: https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/
Suggested-by: Thomas Stranger <[email protected]>
Signed-off-by: Fabio Baltieri <[email protected]>
(cherry picked from commit ae0e5b1)
(cherry picked from commit 4d33fc1)

Author: fabiobaltieri

.github/workflows/hello_world_multiplatform.yaml

@@ -28,7 +28,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-22.04, ubuntu-24.04, ubuntu-24.04-arm, macos-13, macos-14, windows-2022]
+        os: [ubuntu-22.04, ubuntu-24.04, ubuntu-24.04-arm, macos-14, windows-2022]
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout