DI: make a test method longer to avoid flakiness

[p-datadog]

What does this PR do?
Changes a method under test for a DI test that asserts on method execution duration to take more time.

Motivation:
Flaky test execution in CI where the previous version (method simply returning an integer) was reported as having zero execution time:

  1) Instrumentation integration log probe method probe when message template references special variables @duration substitutes the expected value
     Failure/Error: expect(value).to be > 0

       expected: > 0
            got:   0.0
     # ./spec/datadog/di/integration/instrumentation_spec.rb:535:in 'block (7 levels) in <top (required)>'
     # ./lib/datadog/di/probe_manager.rb:242:in 'Datadog::DI::ProbeManager#probe_executed_callback'
     # ./lib/datadog/di/instrumenter.rb:218:in 'block (2 levels) in hook_method'
     # ./spec/datadog/di/integration/instrumentation_spec.rb:538:in 'block (6 levels) in <top (required)>'
     # ./spec/spec_helper.rb:274:in 'block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:154:in 'block (2 levels) in <top (required)>'
     # ./spec/support/execute_in_fork.rb:32:in 'ForkableExample#run'

Change log entry
None

Additional Notes:

How to test the change?
Change is in test suite only

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 125.00%
• Total Coverage: 98.52% (+0.01%)

View detailed report

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 6bdf919 | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-11-19 20:09:28

Comparing candidate commit da3bf7c in PR branch flaky-di-test with baseline commit 137add8 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 44 metrics, 2 unstable metrics.