CODETOOLS-7903234: JMH: Improve GHA triggers

[shipilev]

GHA workflows need to have a push-based trigger instead of pull_request one, in order to comply with current scheme of running actions in private forks.

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Progress

• Change must not contain extraneous whitespace
• Change must be properly reviewed (1 review required, with at least 1 Committer)

Issue

• CODETOOLS-7903234: JMH: Improve GHA triggers

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jmh pull/75/head:pull/75
$ git checkout pull/75

Update a local copy of the PR:
$ git checkout pull/75
$ git pull https://git.openjdk.org/jmh pull/75/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 75

View PR using the GUI difftool:
$ git pr show -t 75

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jmh/pull/75.diff

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Webrevs

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