Update github host from macos-13 to macos-15

macos-13 is no more available
https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/

it is causing a lot of PR jobs to wait in queue for a long time when
there is a PR on 4.1 branch

it has been already upgraded on main branch

Signed-off-by: Aurélien Pupier <apupier@ibm.com>

Author: apupier

.github/workflows/build-thirdparty.yml

@@ -175,7 +175,7 @@ jobs:
     name: Build Third Party Libraries (macOS)
     needs: changes
     if: ${{ needs.changes.outputs.thirdparty_changes == 'true' }}
-    runs-on: macos-13
+    runs-on: macos-15
     steps:
       - name: Checkout ${{ github.ref }}
         uses: actions/checkout@v4