[IMPROV] Allow workflows to run on forks, except for test targets

[AlexVCaron]

Type of improvement

If submitting a new module or fixing a bug, please use the appropriate template.

• Documentation
• Development tools (e.g. linter, formatter, etc.)
• Development container
• Global update (please specify)
• Other (please specify)

Describe your improvement

Remove the restrictions on update_pr and update_main workflows to allow them to run on other repos than scilus/nf-scil. Still, block execution of the test sub-workflow so self-hosted runners aren't used.

Describe how to test your improvement

1. Create a fork
2. Rebase your fork's branch on this PR
3. Push online and open a PR ON YOUR FORK
4. Check that the workflow triggers and that the tests are skipped

Checklist before requesting a review

• Ensure the syntax is correct (EditorConfig and Prettier must pass)
• Run the test suites if your changes affect any module
• Regenerate the Poetry lock file if you have updated the dependencies
• Ensure the documentation is up-to-date