Support Sinatra 3

[TonyCTHsu]

What does this PR do?

Create Sinatra's appraisal group avoids the version update be blocked. Hence we could include Sinatra 3 into our test suite.

[codecov-commenter]

Codecov Report

Merging #2360 (bfd0c3b) into master (97885d7) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2360      +/-   ##
==========================================
+ Coverage   98.34%   98.36%   +0.02%     
==========================================
  Files        1102     1101       -1     
  Lines       58942    58873      -69     
==========================================
- Hits        57967    57911      -56     
+ Misses        975      962      -13     

Impacted Files	Coverage Δ
...adog/tracing/contrib/sidekiq/client_tracer_spec.rb	97.91% <0.00%> (-2.09%)	⬇️
...adog/tracing/contrib/sidekiq/server_tracer_spec.rb	99.16% <0.00%> (-0.84%)	⬇️
...ng/contrib/active_support/cache/instrumentation.rb	87.67% <0.00%> (+0.08%)	⬆️
lib/datadog/core/diagnostics/environment_logger.rb	99.21% <0.00%> (+0.78%)	⬆️
lib/datadog/core/workers/polling.rb	100.00% <0.00%> (+3.44%)	⬆️

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[ivoanjo]

Out of curiosity, does the Sinatra 3 integration need no changes? I somehow got the impression that we'd need to fix something to get it working.

[TonyCTHsu]

@ivoanjo I setup an integration application some weeks ago when Sinatra 3 is released. It just worked!

This PR is mainly addressing the fact that we are using Sinatra 3 in our test suite instead of 2.

[ivoanjo]

@ivoanjo I setup an integration application some weeks ago when Sinatra 3 is released. It just worked!

This PR is mainly addressing the fact that we are using Sinatra 3 in our test suite instead of 2.

Awesome, glad to hear it! :)