Card labels should not open sidebar

What does this MR do?

This MR prevent the sidebar opening event when a card label is clicked #208867 (closed).
My approach was to change the @mouseup board card event to @click and to add a .stop modifier to the label click event.
The problem with this MR is that the dropdown is fired after clicking on the label and I don't think it is the expected behaviour.

/cc @sstern

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
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Availability and Testing

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• Tested in all supported browsers
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Security

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