Migrate font weight utilities to Tailwind in ee/app/**/*.haml

What does this MR do and why?

Related #456641 (closed)

This migrates font-weight utilities to Tailwind variant:

• gl-font-weight-normal -> gl-font-normal
• gl-font-weight-bold -> gl-font-bold

in *.haml files in directory ee/app/.

MR acceptance checklist

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Screenshots or screen recordings

gl-font-bold in ee/app/views/groups/settings/_restore.html.haml

gl-font-normal in ee/app/views/projects/mirrors/_branch_filter.html.haml

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