Add `get_embedding` for `GeneralUnitaryMultiplicationGroup`

[mateuszbaran]

This is needed for example by extrinsic mean calculation.

I've also added compat entries for stdlibs as written here: https://github.com/JuliaRegistries/General/pull/94151.

[codecov[bot]]

Codecov Report

Merging #670 (fa6c103) into master (4fce452) will increase coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #670      +/-   ##
==========================================
+ Coverage   99.36%   99.40%   +0.03%     
==========================================
  Files         108      108              
  Lines       10597    10599       +2     
==========================================
+ Hits        10530    10536       +6     
+ Misses         67       63       -4     

Files	Coverage Δ
src/groups/general_unitary_groups.jl	100.00% <100.00%> (ø)
src/groups/special_orthogonal.jl	100.00% <ø> (ø)

... and 2 files with indirect coverage changes

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[kellertuer]

You could still copy over the new action for the News.md change check and if you like even the new make.jl args if you like

[mateuszbaran]

I've added the action but I will leave make.jl changes for later. I will try to fix the new bug first but today I'm too tired to figure it out.

[kellertuer]

No problem, I can also do the make.jl in a later PR.