[jdk21u] RFR: 8315062: [GHA] get-bootjdk action should return the abolute path

[Aleksey Shipilev]

Clean backport to improve GHA reliability and keep testing pipelines in sync.

Additional testing:
 - [ ] GHA

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Commit messages:
 - Backport 99ea8bf2b962011e57d02a93217d65d7259e8f80

Changes: https://git.openjdk.org/jdk21u/pull/247/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=247&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315062
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u/pull/247.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/247/head:pull/247

PR: https://git.openjdk.org/jdk21u/pull/247