RFR: 8282944: GHA: Add Alpine Linux x86_64 pre-integration check

[George Adams]

Adds Alpine build CI job to the GitHub actions matrix. Currently this only builds hotspot. I can add tests too if people think that would be useful but for now I've left it as just build.

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Commit messages:
 - fix test bundle
 - add make-target: 'hotspot'
 - 8282944: GHA: Add Alpine Linux x86_64 pre-integration check

Changes: https://git.openjdk.org/jdk/pull/20577/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20577&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8282944
  Stats: 140 lines in 3 files changed: 139 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20577.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20577/head:pull/20577

PR: https://git.openjdk.org/jdk/pull/20577