Fix lint errors in Rust 1.73 and 1.74

[edmorley]

Fixes the following new error in Rust 1.73:

$ RUSTDOCFLAGS="-D warnings" cargo doc --all-features --document-private-items --no-deps
...
error: redundant explicit link target
  --> libcnb-test/src/test_runner.rs:35:34
   |
35 |     /// signalled via [`Result`](Result) values. Instead, this function panics whenever an unexpected error
   |                        --------  ^^^^^^ explicit target is redundant
   |                        |
   |                        because label contains path that resolves to same destination
   |
   = note: when a link's destination is not specified,
           the label is used to resolve intra-doc links
   = note: `-D rustdoc::redundant-explicit-links` implied by `-D warnings`
help: remove explicit link target
   |
35 |     /// signalled via [`Result`] values. Instead, this function panics whenever an unexpected error
   |                       ~~~~~~~~~~
...

And errors like these in Rust 1.74:

$ cargo clippy --all-targets
warning: unnecessary hashes around raw string literal
  --> libcnb-package/src/cross_compile.rs:21:17
   |
21 | /                 r#"For cross-compilation from macOS to x86_64-unknown-linux-musl, a C compiler and
22 | | linker for the target platform must be installed on your computer.
23 | |
24 | | The easiest way to install the required cross-compilation toolchain is to run:
...  |
27 | | For more information, see:
28 | | https://github.com/messense/homebrew-macos-cross-toolchains"#,
   | |_____________________________________________________________^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_raw_string_hashes

GUS-W-14249508.