[jdk8u-dev] RFR: 8369226: GHA: Switch to MacOS 15

[Andrew John Hughes]

This is a backport of [JDK-8369226](https://bugs.openjdk.org/browse/JDK-8369226) from 11u that upgrades from macos-13 to macos-15-intel, and XCode from 14.3.1 to 16.4, as MacOS 13 runners are now unavailable.

Due to the different structure of the GHA support in 8u, and the absence of aarch64 on MacOS, this is a backport in spirit rather than a 1:1 relationship, with the same values being changed in their different locations in the 8u `submit.yml`.

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Depends on: https://git.openjdk.org/jdk8u-dev/pull/740

Commit messages:
 - Backport 1b0f612e5e08cfa1581cf22433b36b5f075c0f23

Changes: https://git.openjdk.org/jdk8u-dev/pull/738/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=738&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369226
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/738.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/738/head:pull/738

PR: https://git.openjdk.org/jdk8u-dev/pull/738