deps: update undici to 7.21.0 #3100

Job	Run time
Build slim tarball	1m 35s
aarch64-darwin: with shared libraries	38m 20s
x86_64-linux: with shared libraries	48m 52s
aarch64-linux: with shared libraries	1h 25m 22s
x86_64-darwin: with shared libraries	1h 7m 3s
	4h 1m 12s

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