RFR: Testing GHA [v4]

[Jorn Vernee]

> Add a basic actions workflow that runs the tests on pull requests

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Set sepcific ubuntu version

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Changes:
  - all: https://git.openjdk.java.net/jextract/pull/6/files
  - new: https://git.openjdk.java.net/jextract/pull/6/files/998e2adc..e82f6f7f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jextract&pr=6&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jextract&pr=6&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jextract/pull/6.diff
  Fetch: git fetch https://git.openjdk.java.net/jextract pull/6/head:pull/6

PR: https://git.openjdk.java.net/jextract/pull/6