Upgrade poise current to include poise next and serenity-next (#224) #925

Job	Run time
Rustfmt	14s
Build docs	2m 41s
Clippy	53s
Test (MSRV)	1m 15s
Test (stable)	2m 5s
Test (beta)	1m 57s
Test (nightly)	1m 58s
Test (macOS)	6m 56s
Test (Windows)	3m 53s
Test (no features)	1m 15s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 20s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 24s
	25m 51s

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