deps: update undici to 7.21.0 #3078

Job	Run time
Build slim tarball	1m 32s
x86_64-darwin: with shared libraries	1h 44m 47s
aarch64-darwin: with shared libraries	33m 11s
x86_64-linux: with shared libraries	49m 58s
aarch64-linux: with shared libraries	1h 26m 49s
	4h 36m 17s

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