RFR: 8291444: GHA builds/tests won't run manually if disabled from automatic running

[Christoph Langer]

This is an attempt to fix the issue reported in JDK-8291444.

The check for secrets.JDK_SUBMIT_FILTER should only be applied to the push event but not on e.g. workflow_dispatch.
Currently setting JDK_SUBMIT_FILTER would lead to setting every platform to 'false', even when manually triggering the GHA run via workflow_dispatch.

I furthermore propose to relax the check for unknown events. In OpenJDK we only use/define workflow_dispatch and push. Other events would hence not trigger the workflow anyway. However, downstream vendors (like us in SapMachine) might use other events such as pull_request and they would then need to patch this away. This kind of downstream issue was also reported by [Amazon](https://mail.openjdk.org/pipermail/build-dev/2022-August/035102.html). If you agree, I would remove the commented lines 91-93. Otherwise I have to uncomment them.

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Commit messages:
 - JDK-8291444

Changes: https://git.openjdk.org/jdk/pull/11365/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11365&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291444
  Stats: 17 lines in 1 file changed: 7 ins; 6 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/11365.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11365/head:pull/11365

PR: https://git.openjdk.org/jdk/pull/11365