Add ostruct to Gemfile for Ruby >= 3.3.5

[y9v]

This addresses the deprecation warning that ostruct will not be part of standard library since ruby 3.5

What does this PR do?
This PR adds ostruct gem to Gemfile for Ruby version 3.3.5 and higher.

Motivation:
Failing tests due to a deprecation warning:
https://github.com/DataDog/dd-trace-rb/actions/runs/10703793866/job/29675192240?pr=3887

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.86%. Comparing base (ae50107) to head (f4c0c4e).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3890   +/-   ##
=======================================
  Coverage   97.85%   97.86%           
=======================================
  Files        1277     1277           
  Lines       76392    76392           
  Branches     3744     3744           
=======================================
+ Hits        74757    74764    +7     
+ Misses       1635     1628    -7     

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[pr-commenter]

Benchmarks

Benchmark execution time: 2024-09-05 10:32:41

Comparing candidate commit f4c0c4e in PR branch fix-ostruct-deprecation-warning with baseline commit ae50107 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 23 metrics, 2 unstable metrics.

[ivoanjo]

Minor: I suggest maybe doing >= 3.3 instead of 3.3.5.

My thinking is that we're not very consistent in upgrading to point releases in our different test/development environments, and on the off chance we have some weird issue from this, it may be a bit harder to diagnose if only some of the 3.3 series gets this new version.

[y9v]

fixed here 261b590 (force pushed)

[ivoanjo]

This looks good... But there's one more missing piece. Specifically, this will affect the appraisal gemfiles for 3.3 rubies.

Supposedly we have a Github Action that should trigger to update this, but the trigger condition is buggy (found this recently) and sometimes doesn't trigger when it should (e.g. in this PR): https://github.com/DataDog/dd-trace-rb/actions/runs/10716765010/job/29715426163 .

As a quick workaround, I've opened another PR (#3892) to force the GHA to trigger: https://github.com/DataDog/dd-trace-rb/actions/runs/10717020845/job/29715869065 .

It's currently running, and once it's done, we can cherry-pick that change on top of this PR.

[y9v]

@ivoanjo thanks! I haven't thought about this.

[ivoanjo]

👍 LGTM

[ivoanjo]

@ivoanjo thanks! I haven't thought about this.

No worries! Our setup is quite complex to try to cover all the testing we need, and it has a few gaps that we haven't yet plugged :)

I've cherry-picked the commit generated by GHA, I think we're good to go once CI is green and beautiful :)