Disable dependents toggle in plugin manager with system read

[timja]

It was reported as jenkinsci/dark-theme-plugin#258 although nothing to do with dark theme.
One of the tds has some metadata added with display:none which was being excluded by the isAdmin check.

This narrows the isAdmin down so dependents and dependencies correctly show up in the metadata

Testing done

Tested with system read:

Tested with admin:

Proposed changelog entries

• Correct styling for plugins that can't be disabled in plugin manager when user has system read permission.

Proposed upgrade guidelines

N/A

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[NotMyFault]

Tests are failing

[timja]

minor fix I noticed while checking this again, tests were logging a giant stacktrace, this button is only on the updates page and not the installed page so its event listener shouldn't be active

[timja]

/label ready-for-merge

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This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!