Eliminates minor javascript error in toolbar popup button

[dgrammatiko]

Whenever a modal is render through a toolbar popup button, an error is logged in the browser.

This is due to onClick been set as Url.

This PR changes onclick to value (acceptable option for buttons)

Testing

Apply #5386
There are two javascript errors logged in your browsers console (the second one Joomla.toggleSidebar is solved #5259)
Apply this PR
error should go away

[smanzi]

@dgt41 confirmed issues and fixing by respective PRs
@test success

[roland-d]

@test all good and fixes also a JS error on the banner tracks export.

[roland-d]

Moving to RTC, we have 2 successful tests.

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