[NO-TICKET] Fix flaky profiling spec "expect(sample_count).to be > 0", got nil

[ivoanjo]

What does this PR do?

This PR fixes the flaky profiling spec we saw in
https://github.com/DataDog/dd-trace-rb/actions/runs/28523919081/job/84555219767 :

Failures:

  1) Datadog::Profiling::Collectors::CpuAndWallTimeWorker#start when using the no signals workaround always simulates signal delivery
     Failure/Error: expect(sample_count).to be > 0

       expected: > 0
            got:   nil
     # ./spec/datadog/profiling/collectors/cpu_and_wall_time_worker_spec.rb:699:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:313:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:207:in `block (2 levels) in <top (required)>'
     # /usr/local/bundle/gems/webmock-3.26.2/lib/webmock/rspec.rb:39:in `block (2 levels) in <top (required)>'
     # /usr/local/bundle/gems/rspec-wait-0.0.10/lib/rspec/wait.rb:47:in `block (2 levels) in <top (required)>'
     # ./spec/support/execute_in_fork.rb:32:in `run'

Finished in 17.45 seconds (files took 0.96839 seconds to load)
812 examples, 1 failure, 113 pending

Failed examples:

rspec ./spec/datadog/profiling/collectors/cpu_and_wall_time_worker_spec.rb:678 # Datadog::Profiling::Collectors::CpuAndWallTimeWorker#start when using the no signals workaround always simulates signal delivery

TL;DR the problem here is that when this spec was written,

        all_samples = try_wait_until do
          samples = samples_from_pprof_without_gc_and_overhead(recorder.serialize!)
          samples if samples.any?
        end

If you saw any samples that were NOT GC and NOT overhead, then for sure you were seeing a regular "sampled all the threads" event, and thus the current thread was for sure going to be in there.

This is no longer the case now that we have a mechanism for special-casing internal profiler threads and threads without the GVL (as well as sometimes leftover state -- that's being addressed in #5960 ).

Thus the TL;DR as far as this test cares, it can't just assume that if there's any samples in there, those would be the samples it's expecting to get.

To fix this, we check that we have samples for the current thread, which was the underlying assumption/expectation that wasn't being stated.

Motivation:

Zero flakiness in profiling!

Change log entry

None.

Additional Notes:

There were a few other specs that we changed recently for similar reasons -- they were written in simpler times ;)

Also, I gave a pass overall on this file to make sure there weren't other specs encoding the same wrong assumption that would flake in the future but as far as I saw, this is the last one.

How to test the change?

Green CI

[datadog-datadog-prod-us1]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 90.02% (-0.01%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 26ce6d8 | Docs | Datadog PR Page | Give us feedback!}