Make BitBucket import button Pajamas compliant

What does this MR do and why?

Make button in template app/views/import/bitbucket_server/new.html.haml Pajamas compliant.

Credit goes to @ya332 for his work in !126017 (merged).

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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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• I have evaluated the MR acceptance checklist for this MR.

Related to #416025 (closed)