Increase iterations of flaky benchmarks

[PROFeNoM]

Description

Three benchmarks appear to be flaky:

PHPRedisBench/benchRedisBaseline
ContextPropagationBench/benchExtractHeaders128Bit
PHPRedisBench/benchRedisOverhead

Following @ddyurchenko's recommendations, increase the iteration count of these subjects to 15.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-01-11 09:12:02

Comparing candidate commit 948f0f7 in PR branch alex/bench/flaky with baseline commit 4568c41 in branch master.

Found 2 performance improvements and 0 performance regressions! Performance is the same for 39 metrics, 49 unstable metrics.

scenario:ContextPropagationBench/benchExtractHeaders128Bit

• 🟩 execution_time [-1138.508ns; -394.825ns] or [-15.180%; -5.264%]

scenario:ContextPropagationBench/benchExtractTraceContext64Bit

• 🟩 execution_time [-715.063ns; -184.937ns] or [-9.931%; -2.569%]