fix(scopes): Add more typing info to Scope.update_from_kwargs's "contexts"

[Perlence]

The original type hint could be understood as a one-level dict of str to Any, when in fact, it's a two-level dict.

[antonpirker]

Looks good! Thanks for the contribution @Perlence!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.53%. Comparing base (a3b6e5d) to head (a5cc928).
Report is 2 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4080      +/-   ##
==========================================
- Coverage   79.57%   79.53%   -0.04%     
==========================================
  Files         140      140              
  Lines       15512    15512              
  Branches     2628     2628              
==========================================
- Hits        12343    12338       -5     
- Misses       2335     2337       +2     
- Partials      834      837       +3     

Files with missing lines	Coverage Δ
sentry_sdk/scope.py	85.53% <ø> (ø)

... and 2 files with indirect coverage changes