fix(theme): updating bodyBackground color for Teams dark theme

[codepretty]

For reference, #1478 and #1870

**This will create a lot of screener regressions, so any help reviewing or thinking about unintended consequences would be helpful!

[codecov]

Codecov Report

Merging #1961 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1961   +/-   ##
=======================================
  Coverage   70.27%   70.27%           
=======================================
  Files         893      893           
  Lines        7892     7892           
  Branches     2309     2285   -24     
=======================================
  Hits         5546     5546           
  Misses       2333     2333           
  Partials       13       13

Impacted Files	Coverage Δ
...kages/react/src/themes/teams-dark/siteVariables.ts	100% <100%> (ø)	⬆️

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[levithomason]

@codepretty, I went through all 142 screener diffs ( 😅) and confirmed only the background color was affected.

This was almost always just the body color except for two items:

1. In the case of some menu examples the ul element also changed its background color. I believe this is correct and intentional however as the Menu element takes on the body background color.
2. Some SVG elements seem to be triggering a diff, but the glyphs look identical to my eye.

Example diff showing these two issues can be seen here.

I think it is safe to merge.