Bump Jenkins and bom version to 2.387.x

[mifitous]

Testing done

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[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/