Bump Jenkins and bom version to 2.387.x

[mifitous]

Testing done

### Submitter checklist
- [ ] Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!
- [ ] Ensure that the pull request title represents the desired changelog entry
- [ ] Please describe what you did
- [ ] Link to relevant issues in GitHub or Jira
- [ ] Link to relevant pull requests, esp. upstream and downstream changes
- [ ] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[jmini]

Some notes about this change:

The BOM update is requested, in order to get version 5.3.0-88.vf8787b_92d679 of the gitlab-api plugin.

According to PR jenkinsci/bom#2121 the bom bom-2.361.x will never be updated anymore. So we need to switch to a newer one.

[jetersen]

@jmini
You can read more about choosing a Jenkins version baseline here:
https://www.jenkins.io/doc/developer/plugin-development/choosing-jenkins-baseline/