Migrate font weight utilities to Tailwind in 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-semibold -> gl-font-semibold
• gl-font-weight-bold -> gl-font-bold

in *.haml files in directory app/.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

gl-font-normal and gl-font-bold in app/components/pajamas/single_stat_component.html.haml

gl-font-semibold in app/views/projects/triggers/_index.html.haml

How to set up and validate locally