RFR: 8338286: GHA: Demote x86_32 to hotspot build only

[Aleksey Shipilev]

As planned in [JDK-8338285](https://bugs.openjdk.org/browse/JDK-8338285), we are about to deprecate the port for removal. It makes little sense to continue testing the port, and thus block development and integration of new features.

Ahead of that JEP, we can separately decide to disable the x86-32 test jobs in GHA. This effectively demotes x86-32 to any other port that only builds Hotspot and relies on port maintainers to provide the runtime testing. This is deliberately separate change, so that Update Releases could decide to disable their x86-32 jobs as well.

-------------

Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/20563/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20563&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338286
  Stats: 19 lines in 1 file changed: 1 ins; 11 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/20563.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20563/head:pull/20563

PR: https://git.openjdk.org/jdk/pull/20563