Fix minor typo in protocols.md #5853

Job	Run time
Test Coverage	45s
Build (feature permutations)	3m 42s
Build Standard Binary (nightly)	40s
Build (stable MSRV)	27s
Lints	1m 2s
Unit + Doc Tests (Miri)	1m 41s
Nightly (build, test, doc)	2m 34s
Unit + Doc Tests	1m 35s
Integration Test (AArch64)	1m 17s
Integration Test (IA-32)	1m 36s
Integration Test (x86_64)	1m 46s
Integration Test (x86_64 Windows)	4m 7s
	21m 12s

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