fix(falcon): Don't exhaust request body stream

[szokeasaurusrex]

Only read the cached request._media, since reading request.media will exhaust the request.bounded_stream if it has not been read before. Note that this means that we will now only send the JSON request body to Sentry if the Falcon request handler reads the JSON data.

Fixes #3761

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.87%. Comparing base (3e28853) to head (83334b7).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3768      +/-   ##
==========================================
- Coverage   79.90%   79.87%   -0.04%     
==========================================
  Files         137      137              
  Lines       15373    15373              
  Branches     2608     2609       +1     
==========================================
- Hits        12284    12279       -5     
- Misses       2221     2223       +2     
- Partials      868      871       +3     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/falcon.py	85.49% <100.00%> (ø)

... and 3 files with indirect coverage changes

[antonpirker]

Looks good!