RFR: Testing GHA

[Jorn Vernee]

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

-------------

Commit messages:
 - Use Oracle JDK
 - Back to repo hosted acitons
 - Update test.yml
 - Change actions to run in fork instead
 - Remove java check from test run
 - Typo
 - Add missing blank lines
 - Checkout specific jtreg tag
 - Working Impl
 - Remove whitespace
 - ... and 2 more: https://git.openjdk.java.net/jextract/compare/e6345e3a...c3d97f9a

Changes: https://git.openjdk.java.net/jextract/pull/6/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jextract&pr=6&range=00
  Stats: 64 lines in 1 file changed: 64 ins; 0 del; 0 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