Upgrade from deprecated macos-13 to macos-15-intel in CI

[cclauss]

Replace GitHub Actions runner image macos-13 with macos-15-intel as recommended in:

• https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down

The macOS 13 runner image will be retired by December 4th, 2025.

The currently available GitHub Actions macOS runners are:

macOS Version	runner.arch
macos-13	X64
macos-14	ARM64
macos-15	ARM64
macos-15-intel	X64
macos-26	ARM64
macos-latest	ARM64

NO AI WAS USED TO CREATE THIS PULL REQUEST.

@garydgregory

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[sebbASF]

AFAIK, macos-13 was only available for intel; there is no particular reason to stick with Intel rather than choosing the new default architecture which is Arm64.
So macos-14, -15 or -latest would be fine.

Also, macos-26 is probably a typo for macos-16

[bindul]

AFAIK, macos-13 was only available for intel; there is no particular reason to stick with Intel rather than choosing the new default architecture which is Arm64.

So macos-14, -15 or -latest would be fine.

Also, macos-26 is probably a typo for macos-16

Apple moved to a unified year based versions across all its OSes. All major releases for MacOS, iOS, WatchOS, etc. released this year (September on) use major version number 26.

https://support.apple.com/en-us/109033

[cclauss]

Please review an alternative approach:

• Upgrade from deprecated macos-13 to macos-latest in CI #591

[ppkarwasz]

I also would prefer to upgrade to macos-latest. There is only one catch for that: there is no Temurin JDK 8 version for ARM64, so:

• we either need to switch to another distribution (e.g. zulu), or

• we need to use zulu for just that specific case:

  - name: Set up JDK ${{ matrix.java }}
    uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
    with:
      distribution: ${{ runner.arch == 'ARM64' && matrix.java == '8' && 'zulu' || 'temurin' }}
      java-version: ${{ matrix.java }}

[cclauss]

Closing in favor of:

• Upgrade from deprecated macos-13 to macos-latest in CI #591