[crac] RFR: Disable non-buildable platforms in GHA

[Anton Kozlov]

Disable builds on GitHub Actions for platforms that is not expected to build successfully. The change removes GHA failures noise in forks of the project repo. https://github.com/AntonKozlov/crac/actions/runs/2109490740

I've also requested GHA to be enabled to the project repo, so tests report should appear for this PR.

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Commit messages:
 - Disable non-buildable platforms in GHA

Changes: https://git.openjdk.java.net/crac/pull/20/files
 Webrev: https://webrevs.openjdk.java.net/?repo=crac&pr=20&range=00
  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/crac/pull/20.diff
  Fetch: git fetch https://git.openjdk.java.net/crac pull/20/head:pull/20

PR: https://git.openjdk.java.net/crac/pull/20