[JENKINS-72505] f:validateButton finds selected radio button

[timja]

See JENKINS-72505.

Previously it just found the last button when doing validation that involved a radio button, it should try and find a selected one instead...

Noticed in jenkinsci/azure-vm-agents-plugin#493

Testing done

Unit test, if you run it on master you get:

   4.505 [id=25]	WARNING	h.i.i.InstallUncaughtExceptionHandler#handleException: Caught unhandled exception with ID 03a79f27-87f9-4111-a5bc-403a8e405e76
org.junit.ComparisonFailure: expected:<[]f> but was:<[reallynot]f>

Manually:

Tested with a validateButton when editing a template in an azure cloud jenkinsci/azure-vm-agents-plugin#493.
Previously the last radio button was being sent to the method handling the validate button, now it's the selected radio.
I also added an extra radio button locally to make sure it wasn't just taking the first one in the dom by continuing all the way.

Proposed changelog entries

• JENKINS-72505, Find selected radio option when validating instead of the last one

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N/A

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[timja]

@jenkinsci/core-pr-reviewers possible to get a review for this simple bug please?

[aneveux]

LGTM, thanks a lot for the fix!

[MarkEWaite]

This PR is now ready for merge. We will merge it after approximately 24 hours if there is no negative feedback.

/label ready-for-merge