Restrict trigger push branch for GitHub Workflow

[apupier]

Feature branches rarely need their own CI runs: the code is already tested when a pull request is opened against a release branch. If the push trigger has no branch restriction and pull_request is also configured, every push to a branch with an open PR runs the workflow twice: once for the push and once for the PR synchronisation.

Always give the push trigger an explicit list of branches: this stops branches created from a release branch from inheriting its workflow runs.

see https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=430408443#GitHubActionsRecommendedPractices-Restrictthepushtriggertospecificbranches

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[apupier]

build error on CI check is unrelated to this PR:

[79](https://github.com/apache/commons-jcs/actions/runs/28573288833/job/84715788817#step:5:780)
Error:  Failed to execute goal org.apache.maven.plugins:maven-javadoc-plugin:3.12.0:javadoc (default-cli) on project commons-jcs4-jcache: An error has occurred in Javadoc report generation: Project contains Javadoc Warnings -> [Help 1]