[jdk11u-dev] RFR: 8340671: GHA: Bump macOS and Xcode versions to macos-12 and XCode 13.4.1

[Antonio Vieiro]

The macos-11 github runners [were deprecated and removed in June 2024](https://github.blog/changelog/2024-05-20-actions-upcoming-changes-to-github-hosted-macos-runners/) , making the macos tests to hang in openjdk11u-dev (and other OpenJDK repositories).

[JDK-8335793 GHA: Bump macOS and Xcode versions](https://bugs.openjdk.org/browse/JDK-8335793) upgraded the version https://github.com/openjdk/jdk11u-dev/pull/2835 of mac runners to macos-13. This upgrade in github runners required a long list of changes in openjdk11u-dev that proved difficult to review.

In order to ease the review process this PR downgrades the version of github runners in jdk11u-dev from the current macos-13 to macos-12 and xcode-13.4.1. This will require a single backport of [JDK-8299254 Support dealing with standard assert macro](https://bugs.openjdk.org/browse/JDK-8299254) (a follow-up to this PR), making the review process easier.

Once the github actions are running again in macos-12 an upgrade to macos-13 could be performed, if required, with some more additional PRs.

-------------

Commit messages:
 - 8340671: GHA: Bump macOS and Xcode versions to macos-12 and XCode 13.4.1

Changes: https://git.openjdk.org/jdk11u-dev/pull/2940/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2940&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340671
  Stats: 5 lines in 3 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2940.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2940/head:pull/2940

PR: https://git.openjdk.org/jdk11u-dev/pull/2940