github-actions: filter by current active branches in the repository

[v1v]

What does this PR do?

Filter by the current active branches in elastic/elastic-agent

Why is it important?

https://github.com/elastic/oblt-actions/tree/v1/elastic/active-branches supports now filtering the branches from the Unified Release that are available in this repository.

This can help with cases when the release branch has not been created yet

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

How to test this PR locally

I ran https://github.com/elastic/elastic-agent/actions/runs/12314405668

Related issues

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[rowlandgeoff]

skip-ci is essentially ineffective since we have required checks. If they're required and we skip them, we're stuck.

[rowlandgeoff]

/test

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube