fix: elevate CSS specificity for BS5 radio/checkbox group label margin

[elnelson575]

Summary

• Bumps CSS specificity on bslib's BS5 radio/checkbox group label-spacing rule by doubling the class (.shiny-input-radiogroup.shiny-input-radiogroup) — a Garrick-suggested idiom that signals "this is purely for specificity" without changing which elements are matched.
• This makes bslib's rule win the specificity tie against Shiny's inline-specific override (.shiny-input-radiogroup.shiny-input-container-inline), so inline radio/checkbox groups now use the same calculated label-to-options spacing as their stacked counterparts.
• Rebuilt inst/css-precompiled/5/bootstrap.min.css from the updated SCSS.
• Adds NEWS entries for this fix and for fix: fix bs5 chevron on selectInput(selectize=FALSE) #1307 (BS5 selectInput(selectize = FALSE) chevron fix).

What changes visually

Stacked (vertical / many-choice) groups are unchanged. Inline groups gain ~2px of breathing room between the group label and the first option so all three variants are consistent.

Computed margin-top on .shiny-options-group:

	main	this PR
Vertical	−3.4px	−3.4px
Inline	−1px	−3.4px
Many	−3.4px	−3.4px

Before (main)

After (this PR)

Test plan

• Verify vertical radioButtons() label spacing is unchanged
• Verify inline radioButtons() label spacing now matches vertical
• Verify vertical checkboxGroupInput() label spacing is unchanged
• Verify inline checkboxGroupInput() label spacing now matches vertical

[gadenbuie]

A trick that I like to use for increasing specificity without changing the rule is to duplicate the class name. It's unusual, but .foo.foo doubles the specificity of .foo. It also serves as a signal that the extra class is included only for specificity reasons, whereas adding an additional class could fail if the classes change and looks like it's included for semantic reasons.