benchmark: fix destructuring in dgram/single-buffer #4301

Job	Run time
Build slim tarball	2m 9s
aarch64-darwin: with shared libraries	20m 9s
aarch64-linux: with shared libraries	17m 56s
x86_64-darwin: with shared libraries	28m 4s
x86_64-linux: with shared libraries	20m 49s
	1h 29m 7s

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