docs: improve grammar in reth/README.md #476

Job	Run time
geth (linux/arm64, ubuntu-24.04-arm)	3m 3s
geth (linux/amd64, ubuntu-24.04)	3m 39s
reth (linux/arm64, ubuntu-24.04-arm, jemalloc,optimism)	23m 0s
reth (linux/amd64, ubuntu-24.04, jemalloc,asm-keccak,optimism)	29m 28s
nethermind (linux/amd64, ubuntu-24.04)	2m 58s
nethermind (linux/arm64, ubuntu-24.04-arm)	2m 44s
	1h 4m 52s

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