chore: only ignore c++ diagnostics for ddb headers #6970

Performance Gate Passed

⚡ 2 improved benchmarks
✅ 1007 untouched benchmarks
⏩ 1515 skipped benchmarks¹

	Mode	Benchmark	`BASE`	`HEAD`	Efficiency
⚡	Simulation	`bitwise_not_vortex_buffer_mut[128]`	376.1 ns	317.8 ns	+18.36%
⚡	Simulation	`bitwise_not_vortex_buffer_mut[1024]`	535.6 ns	477.2 ns	+12.22%

_{Comparing ad/only-ignore-diagnostics-for-ddb-headers (5f1fb8b) with develop (d08c89b)}

1515 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩