Fix the warning in the docs because of matplotlib.cm deprecations.

(cherry picked from commit 50c3968)

The recent release of Rust 1.66.0 [1] added new on by default clippy rules
which are causing failures when we run the clippy CI job with the new
rust version. This commit updates the code to fix the issues that clippy
has identified which will unblock CI.

[1] https://blog.rust-lang.org/2022/12/15/Rust-1.66.0.html

Starting in the recently released Rust 1.67.0 clippy enabled a new rule
by default, uninlined_format_args [1], which warns when format!() is
used and a variable is not put in the string inline but isntead as a
separate argument in the macro. For example, `format!("{}", foo)`
Instead the rule suggests using the variable inline the format call
(e.g. `format!("{foo}")`. However, with our msrv of 1.56.1
this syntax was not supported. So trying to fix the places the rule is
triggered as suggested will fail to compile with rust 1.56.1. To address
this and solve this for future rust releases and potential new rules this
commit adds a clippy.toml file which sets the msrv for the rustworkx crate
This will by default disable rules that weren't on by default in rust
1.56.1.

[1] https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args

The most recent tox release, 4.0.0, is a major rewrite of the internals
of tox and several things behave quite differently. This new release
is causing CI jobs to fail as something in incompatible with our tox
configuration. This commit pins the tox version we're using in CI to
unblock things until we can update the tox configuration to be
compatible with both the new and old versions of tox.