Culprit:
(1) - validation/validate.jelly#L58
(2) - validation/validate.jelly#L71

Reproduction steps:

• Install LDAP or clone https://github.com/jenkinsci/ldap-plugin and then mvn hpi:run
• Go to Manage Jenkins > Security
• Select "LDAP" as your Security Realm
• Click on "Test LDAP settings" (1)
  (2) I didn't quickly found it, but it should also be in this page.

Screenshot attached about where the feature is displayed.

Proposal
https://www.jenkins.io/doc/developer/security/csp/#inline-event-handlers

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