RFR: 8341097: GHA: Demote Mac x86 jobs to build only

[Aleksey Shipilev]

See the discussion in the bug. I think we can stop testing Mac x86 in GHA, leaving only the build jobs.

Additional testing:
 - [x] GHA passes

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/21257/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21257&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341097
  Stats: 11 lines in 1 file changed: 0 ins; 11 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21257.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21257/head:pull/21257

PR: https://git.openjdk.org/jdk/pull/21257