Fix net-http tracing's span nesting issue

[st0012]

As mentioned in #1723 (comment), net-http spans should attach to the current span instead of always the top-level transaction.

[codecov-commenter]

Codecov Report

Merging #1796 (dac0bc3) into master (942f645) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1796      +/-   ##
==========================================
+ Coverage   98.41%   98.42%   +0.01%     
==========================================
  Files         145      145              
  Lines        8576     8588      +12     
==========================================
+ Hits         8440     8453      +13     
+ Misses        136      135       -1     

Impacted Files	Coverage Δ
sentry-ruby/lib/sentry/net/http.rb	100.00% <100.00%> (ø)
sentry-ruby/spec/sentry/net/http_spec.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/core_ext/object/deep_dup.rb	100.00% <0.00%> (+5.88%)	⬆️

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