[3.14] gh-153631: Move to macos-26 runner for iOS (GH-153632)

Switches iOS CI to use the macos-26 runner, and makes a small change to the iOS
build script to improve build stability. xcodebuild doesn't guarantee that the
CoreSimulatorService is running before starting a simulator. If the service
isn't running, xcodebuild reports that no simulators are available, and fails to
start the test app. However, simctl blocks until the simulator is available, and
simctl is used to evaluate the default simulator. So - the iOS build script now
unconditionally determines the default simulator, even if a specific simulator
is requested.
(cherry picked from commit 2dc1a91)

Co-authored-by: Russell Keith-Magee <russell@keith-magee.com>

Author: freakboy3742

.github/workflows/build.yml

@@ -387,23 +387,14 @@ jobs:
     needs: build-context
     if: needs.build-context.outputs.run-ios == 'true'
     timeout-minutes: 60
-    runs-on: macos-14
+    runs-on: macos-26
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           persist-credentials: false
 
-      # GitHub recommends explicitly selecting the desired Xcode version:
-      # https://github.com/actions/runner-images/issues/12541#issuecomment-3083850140
-      # This became a necessity as a result of
-      # https://github.com/actions/runner-images/issues/12541 and
-      # https://github.com/actions/runner-images/issues/12751.
-      - name: Select Xcode version
-        run: |
-          sudo xcode-select --switch /Applications/Xcode_15.4.app
-
       - name: Build and test
-        run: python3 Apple ci iOS --fast-ci --simulator 'iPhone SE (3rd generation),OS=17.5'
+        run: python3 Apple ci iOS --fast-ci
 
   build-emscripten:
     name: 'Emscripten'

Apple/testbed/__main__.py

@@ -271,8 +271,14 @@ def run_testbed(
     update_test_plan(location, platform, args)
     print(" done.")
 
+    # xcodebuild doesn't guarantee that the CoreSimulatorService daemon is
+    # running prior to using a simulator, but calling `xcrun simctl list` does.
+    # Determining the default simulator that *would* be used is a cheap action;
+    # so use that as a way to ensure that the CoreSimulatorService daemon is
+    # running.
+    default_simulator = select_simulator_device(platform)
     if simulator is None:
-        simulator = select_simulator_device(platform)
+        simulator = default_simulator
     print(f"Running test on {simulator}")
 
     xcode_test(