Rust 1.45.0 CI job fails to build after latest updates to `serde` and `serde_derive` crates

[ridwanabdillahi]

Describe the bug
The Rust 1.45.0 CI job has started failing due to an update of the serde and serde_derive crates. The latest updates to these crates causes cargo to require the resolver feature which was unstable in the version of cargo shipped in the Rust 1.45.0 toolchain.

This feature was stabilized in the version of cargo shipped with the Rust 1.51.0 toolchain.

Example of failure:

cargo build --all-targets
warning: /src/rust-url/url/Cargo.toml: unused manifest key: package.rust-version
warning: /src/rust-url/data-url/Cargo.toml: unused manifest key: package.rust-version
warning: /src/rust-url/percent_encoding/Cargo.toml: unused manifest key: package.rust-version
warning: /src/rust-url/idna/Cargo.toml: unused manifest key: package.rust-version
warning: /src/rust-url/form_urlencoded/Cargo.toml: unused manifest key: package.rust-version
error: failed to download `serde v1.0.143`

Caused by:
  unable to get packages from source

Caused by:
  failed to parse manifest at `/home/.cargo/registry/src/github.com-1ecc6299db9ec823/serde-1.0.143/Cargo.toml`

Caused by:
  feature `resolver` is required

this Cargo does not support nightly features, but if you
switch to nightly channel you can add
`cargo-features = ["resolver"]` to enable this feature

The Cargo.toml specified in the build failure now includes the manifest key, resolver = "1".

[ridwanabdillahi]

The minimum rust-version for the url crate has been upgraded to 1.51 to ensure clean CI jobs.