updates minimum supported Rust version in Zebrad and rust verison in … #2003

Job	Run time
Generate crates matrix	21s
Check crates matrix	3s
Build zebrad crate	36m 49s
Build zebra-utils crate	16m 31s
Build zebra-test crate	1m 35s
Build zebra-state crate	22m 59s
Build zebra-script crate	3m 30s
Build zebra-scan crate	26m 33s
Build zebra-rpc crate	34m 14s
Build zebra-node-services crate	3m 44s
Build zebra-network crate	6m 52s
Build zebra-grpc crate	14m 50s
Build zebra-consensus crate	17m 36s
Build zebra-chain crate	4m 47s
Build tower-fallback crate	1m 4s
Build tower-batch-control crate	1m 29s
Open or update issues for building crates individually failures	0s
	3h 12m 57s

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