ci: move away from deprecated `actions-rs/toolchain` #471

Job	Run time
Run clippy	45s
Docs	39s
Run clippy for every feature combination	3m 16s
Publish dry run	1m 12s
Rustfmt	11s
Run test suite	1m 5s
Run test suite for `reqwest-middleware` with every feature combination	2m 32s
Run test suite for `reqwest-tracing` with every feature combination	9m 44s
Run test suite for `reqwest-retry` with every feature combination	1m 6s
Spell Check with Typos	4s
	20m 34s

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