benchmark: fix incorrect base64 input in byteLength benchmark #1400

Job	Run time
Build slim tarball	1m 31s
aarch64-linux: with shared libraries	24m 44s
x86_64-linux: with shared libraries	28m 45s
aarch64-darwin: with shared libraries	25m 56s
x86_64-darwin: with shared libraries	47m 22s
	2h 8m 18s

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