* ci: Update actions, replace actions-rs.
* `actions/checkout` is updated from `v1` to the current `v4`.
* `actions-rs/toolchain` is replaced by `dtolnay/rust-toolchain` as
the `actions-rs` actions haven't been maintained in a long time.
* clippy: Remove unnecessary call to `into_iter`.
The parameter takes `IntoIterator`, so we don't have to call
`into_iter` at the call site.
* clippy: Remove explicit lifetime that can be elided.
* clippy: tests: Fix useless conversion warnings.
* clippy: tests: Remove call to `format!`.
* Fix minimal-versions build.
Due to changes in the nightly compiler, using a recent nightly
requires proc-macro2 1.0.60 or later:
https://github.com/dtolnay/proc-macro2/issues/356
* ci: Use is-terminal 0.4.7 for MSRV builds.
is-terminal 0.4.8 updated its MSRV to 1.63, so we can't use it
with our MSRV of 1.56. Force usage of the older version which has
an older MSRV.
Adam Curtis
Bruce Mitchener
Gavrilikhin Daniil
Benjamin Lee
Nathan Whitaker
Tom Parker-Shemilt
Kat Marchán