RFR: Update GHA to jdk20 [v5]

[Maurizio Cimadamore]

> This PR updates the github actions on the jdk20 branch

Maurizio Cimadamore has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Drop macos

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Changes:
  - all: https://git.openjdk.org/jextract/pull/96/files
  - new: https://git.openjdk.org/jextract/pull/96/files/6661c609..b40c8a5c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=96&range=04
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=96&range=03-04

  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jextract/pull/96.diff
  Fetch: git fetch https://git.openjdk.org/jextract pull/96/head:pull/96

PR: https://git.openjdk.org/jextract/pull/96