Fix clippy warnings with newer Rust

[schneems]

Similar to:

• https://github.com/heroku/buildpacks-python/blob/bb0264c8bb0c8b429951c97bf9fdfb894bb78878/Cargo.toml#L15-L16
• heroku/buildpacks-ruby@87c5302

$ cargo clippy --all-targets --all-features -- --deny warnings
    Checking num-rational v0.4.2
   Compiling libcnb-proc-macros v0.22.0 (/Users/rschneeman/Documents/projects/work/libcnb.rs/libcnb-proc-macros)
    Checking libcnb-common v0.22.0 (/Users/rschneeman/Documents/projects/work/libcnb.rs/libcnb-common)
    Checking time v0.3.30
    Checking ahash v0.8.11
    Checking opentelemetry_sdk v0.21.2
error: lint group `pedantic` has the same priority (0) as a lint
  --> Cargo.toml:33:1
   |
33 | pedantic = "warn"
   | ^^^^^^^^   ------ has an implicit priority of 0
34 | unwrap_used = "warn"
   | ----------- has the same priority as this lint
   |
   = note: the order of the lints in the table is ignored by Cargo
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#lint_groups_priority
   = note: `#[deny(clippy::lint_groups_priority)]` on by default
help: to have lints override the group set `pedantic` to a lower priority
   |
33 | pedantic = { level = "warn", priority = -1 }
   |            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[edmorley]

Thank you!