RFR: 8282944: GHA: Add Alpine Linux x86_64 pre-integration check [v11]

[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 two additional commits since the last revision:

 - improve conditional logic
 - try this

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20577/files
  - new: https://git.openjdk.org/jdk/pull/20577/files/4a6cbe47..ab51ba67

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20577&range=10
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20577&range=09-10

  Stats: 21 lines in 1 file changed: 18 ins; 1 del; 2 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