fix: correctly generate types for optional lists #871

Job	Run time
verify-codegen	59s
format	22s
test (async-std-surf)	3m 2s
clippy (async-std-surf)	1m 11s
clippy (tokio-hyper)	1m 14s
clippy (tokio-hyper-rustls)	1m 5s
clippy (tokio-hyper-rustls-webpki)	1m 4s
test (tokio-hyper)	3m 5s
clippy (blocking)	1m 0s
test (tokio-hyper-rustls)	3m 18s
clippy (blocking-rustls)	1m 16s
clippy (blocking-rustls-webpki)	1m 6s
test (tokio-hyper-rustls-webpki)	3m 9s
test (blocking)	3m 1s
test (blocking-rustls)	3m 10s
test (blocking-rustls-webpki)	3m 2s
	31m 4s

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