RFR: 8035: Update Java version in GHA workflow to 11.0.18

[Christoph Langer]

We can bump the GHA JDK to 11.0.18.

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Commit messages:
 - JMC-8035

Changes: https://git.openjdk.org/jmc/pull/465/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=465&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8035
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jmc/pull/465.diff
  Fetch: git fetch https://git.openjdk.org/jmc pull/465/head:pull/465

PR: https://git.openjdk.org/jmc/pull/465