Use Pajamas button

What does this MR do and why?

Resolves

• Migrate to Pajamas compliant buttons in ee/app/... (#417867 - closed)
• Migrate to Pajamas compliant buttons in ee/app/... (#417872 - closed)
• Migrate to Pajamas compliant buttons in app/vie... (#417806 - closed)

Make buttons in several .haml files Pajamas compliant.

Screenshots or screen recordings

File	After migration
app/views/admin/application_settings/_error_tracking.html.haml
ee/app/views/shared/issuable/_filter_weight.html.haml
ee/app/views/registrations/groups/new.html.haml

MR acceptance checklist

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