[jdk21u-dev] RFR: 8325194: GHA: Add macOS M1 testing [v2]

[George Adams]

> Now that macOS M1 executors are [available in GitHub actions](https://github.blog/changelog/2024-01-30-github-actions-introducing-the-new-m1-macos-runner-available-to-open-source/) it makes sense to move the build to run on M1 (rather than cross-compiled) and also enable testing on the platform.

George Adams has updated the pull request incrementally with one additional commit since the last revision:

  work around realpath not working

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Changes:
  - all: https://git.openjdk.org/jdk21u-dev/pull/238/files
  - new: https://git.openjdk.org/jdk21u-dev/pull/238/files/e74f90b6..2a8f9d3d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=238&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=238&range=00-01

  Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/238.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/238/head:pull/238

PR: https://git.openjdk.org/jdk21u-dev/pull/238