RFR: 8282944: GHA: Add Alpine Linux x86_64 pre-integration check [v10]

[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.

George Adams has updated the pull request incrementally with one additional commit since the last revision:

  skip alpine linux build by default

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20577/files
  - new: https://git.openjdk.org/jdk/pull/20577/files/c6906eff..4a6cbe47

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20577&range=09
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20577&range=08-09

  Stats: 2 lines in 1 file changed: 1 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