fix(ci): pin Xcode 26.3.0 for macOS build job

The macOS job in push-event.yml ran on the runner's default Xcode because,
unlike the iOS job, it had no Set up Xcode step. The default Xcode predates
the macOS 26 SDK, so connectivity_plus 7.1.1 failed to compile with:

  value of type 'NWPath' has no member 'isUltraConstrained'

Pin the macOS job to Xcode 26.3.0, matching the iOS job and the macOS job in
pull-request.yml, so the Push workflow builds against the macOS 26 SDK.

Fixes #3284

Author: bhavjsh

.github/workflows/push-event.yml

@@ -250,6 +250,11 @@ jobs:
     needs: common
     runs-on: macos-latest
     steps:
+      - name: Set up Xcode
+        uses: maxim-lobanov/setup-xcode@v1.7.0
+        with:
+          xcode-version: '26.3.0'
+
       - uses: actions/checkout@v6
 
       - name: macOS Workflow