quic: disable building ngtcp2 examples #5705

Job	Run time
Build slim tarball	2m 37s
aarch64-darwin: with shared libraries	2h 21m 6s
aarch64-linux: with shared libraries	1h 26m 51s
x86_64-linux: with shared libraries	1h 59m 8s
x86_64-darwin: with shared libraries	2h 46m 23s
	8h 36m 5s

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