Set Xcode version to 15.1 on macOS arm64 machines

bazel_determinism_test seems to be flaky due to an non-determinsitc issue of the clang compiler in Xcode 14.2

Fixes https://github.com/bazelbuild/bazel/issues/20690

PiperOrigin-RevId: 598760276
Change-Id: Ibc46dfa64fe91f26acfa5091a07c17e3bf97f29c
diff --git a/.bazelci/postsubmit.yml b/.bazelci/postsubmit.yml
index 72fc1a2..1256ab8 100644
--- a/.bazelci/postsubmit.yml
+++ b/.bazelci/postsubmit.yml
@@ -225,6 +225,7 @@
       - build
       - test
   macos_arm64:
+    xcode_version: "15.1"
     shell_commands:
       - sed -i.bak -e 's/^# android_sdk_repository/android_sdk_repository/' -e 's/^#
         android_ndk_repository/android_ndk_repository/' WORKSPACE.bzlmod
diff --git a/.bazelci/presubmit.yml b/.bazelci/presubmit.yml
index 8954f48..6e2c981 100644
--- a/.bazelci/presubmit.yml
+++ b/.bazelci/presubmit.yml
@@ -230,6 +230,7 @@
       - test
   macos_arm64:
     shards: 2
+    xcode_version: "15.1"
     shell_commands:
       - sed -i.bak -e 's/^# android_sdk_repository/android_sdk_repository/' -e 's/^#
         android_ndk_repository/android_ndk_repository/' WORKSPACE.bzlmod