Culprit:
(1) - LabelAxis/config.jelly#L31-L64

Reproduction steps:

• Install Matrix Project or clone https://github.com/jenkinsci/matrix-project-plugin and then mvn hpi:run
• Create a node with a label
• Create a Multi-configuration project
• On the "Configuration Matrix " add an "Agents" axis

Screenshot attached about where the feature is displayed.

Proposal
https://www.jenkins.io/doc/developer/security/csp/#inline-javascript-blocks

Testing notes
 - Ensure to reproduce the feature before any change
 - Ensure that you reproduce the feature after you have made the change