[jfx25u] RFR: 8369140: GHA: Update macOS / x64 build to use macos-15-intel runner

[Kevin Rushforth]

Clean backport of GHA fix to jfx25u.

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Commit messages:
 - Backport e8820e2482bbc00765975854e738fdc214a46ea4

Changes: https://git.openjdk.org/jfx25u/pull/23/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx25u&pr=23&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369140
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jfx25u/pull/23.diff
  Fetch: git fetch https://git.openjdk.org/jfx25u.git pull/23/head:pull/23

PR: https://git.openjdk.org/jfx25u/pull/23