Only run our workflows on the aerius repository

[JornC]

This is part of a round of mass gha workflow refinements, where up to 2 rules are applied:

• Rule 1: a workflow only runs when the repository is aerius/IMAER-java
• Rule 2: a push workflow only triggers on main and the *_fixes branches

For this repo:

Rule 1 is applied to create-release.yml, on-code-push.yml, on-new-tag.yml and on-pull_request-opened-synchronize-reopened.yml
Rule 2 has already been applied

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LLM-generated technical summary

A job-level if: github.repository == 'aerius/IMAER-java' stops the job in any fork while leaving behavior in the canonical repo unchanged. It is deliberately at job level rather than inside the shared composite actions in aerius/github-actions: a composite action has no on: block and can only gate individual steps, so a central version would still spin up the runner and run a full build before declining to publish.

On a pull_request event github.repository is the base repository, so the guard is false only when the PR's base is itself a fork. A PR from a fork into the canonical repo is unaffected.

Note for anyone rehearsing a release in their own fork: a guarded job skips silently rather than failing, so the if: line has to come out locally first.