Perf regression: json_middleware

[pr-benchmarks]

Scenario	Environment	Date	Old RPS	New RPS	Change	Deviation	StDev	Dependencies
json_middleware	Json 400k 5- Trends Intel Win	08/26/2025 19:24:11	10,837	10,629	-1.92 % (-209) 👎	-2.13 σ	98.07	Changes Name Version Diff Json.dll 1.0.0 -> 1.0.0 aspnet/Benchmarks@6bbcf3f...725065d

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