Update docs for 3.4 support

[sarahchen6]

What does this PR do?
Add Ruby 3.4 to the list of compatibilities and update the DevelopmentGuide doc.

Motivation:
Keep our public docs updated to reflect new support.

Change log entry
Yes. Support for Ruby 3.4 is added.

Additional Notes:
N/A

How to test the change?
N/A

[github-actions]

Thank you for updating Change log entry section 👏

^{Visited at: 2025-01-02 15:45:56 UTC}

[datadog-datadog-prod-us1]

Datadog Report

Branch report: sarahchen6/update-compatibility-for-3.4
Commit report: e4c0271
Test service: dd-trace-rb

✅ 0 Failed, 22123 Passed, 1475 Skipped, 4m 59.89s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-03 09:40:45

Comparing candidate commit e4c0271 in PR branch sarahchen6/update-compatibility-for-3.4 with baseline commit e8a6307 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 31 metrics, 2 unstable metrics.

[ivoanjo]

👍 Nice catch on the docs :)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.74%. Comparing base (e8a6307) to head (e4c0271).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4249      +/-   ##
==========================================
- Coverage   97.74%   97.74%   -0.01%     
==========================================
  Files        1355     1355              
  Lines       82366    82365       -1     
  Branches     4230     4230              
==========================================
- Hits        80512    80507       -5     
- Misses       1854     1858       +4     

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