fix: resolve issues with macOS-15 runners (#2607)

* Update iOS support packages to use new-style Xcode runner.

* Explicitly set the Xcode version for macOS runners.

* Correct a download URL.

* Minor tweak to re-trigger CI.

.github/workflows/test.yml

@@ -76,7 +76,7 @@ jobs:
         - os: macos-15-intel
           python_version: '3.13'
           test_select: ios
-        - os: macos-14  # See https://github.com/actions/runner-images/issues/12777
+        - os: macos-15
           python_version: '3.13'
           test_select: ios
         - os: macos-15-intel
@@ -110,6 +110,12 @@ jobs:
       if: runner.os == 'Linux'
       uses: docker/setup-qemu-action@v3
 
+    - name: Set up Xcode
+      if: ${{ startsWith(matrix.os, 'macos-15') }}
+      run: |
+        # GitHub recommends explicitly selecting the desired Xcode version
+        sudo xcode-select --switch /Applications/Xcode_16.4.app
+
     - name: Install dependencies
       run: |
         uv sync --no-dev --group test