Updating copy for Your dashboard heading in main nav

What does this MR do and why?

Updates the copy of the "Your dashboard" heading in the main nav to "Your dashboards", per !96924 (comment 1095539107).

Screenshots or screen recordings

before	after

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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Related to #366082 (closed)