Support Rack 3 by adding to test matrix

[TonyCTHsu]

Motivation:

Support Rack 3

What does this PR do?

1. Rack is tested against version 1, 2, 3
2. Skip Rack 1.x with Ruby 3.3, because non-deprecated form of Regexp.new does not backport to Rack 1.x.
   Fix Regexp deprecated third argument with Regexp::NOENCODING rack/rack#1998

Additional notes

Appsec test requires gem 'rack-contrib' in the group.

[codecov-commenter]

Codecov Report

Merging #3132 (c81c93b) into master (af6e416) will increase coverage by 0.00%.
Report is 12 commits behind head on master.
The diff coverage is 98.52%.

@@           Coverage Diff           @@
##           master    #3132   +/-   ##
=======================================
  Coverage   98.16%   98.16%           
=======================================
  Files        1283     1284    +1     
  Lines       73918    73980   +62     
  Branches     3421     3425    +4     
=======================================
+ Hits        72565    72626   +61     
- Misses       1353     1354    +1     

Files Changed	Coverage Δ
spec/datadog/core/environment/execution_spec.rb	95.79% <94.44%> (-0.32%)	⬇️
lib/datadog/core/environment/execution.rb	100.00% <100.00%> (ø)
lib/datadog/tracing/contrib/rack/header_tagging.rb	100.00% <100.00%> (ø)
...atadog/tracing/contrib/rack/header_tagging_spec.rb	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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