tezos_encoding: useless-format clippy lint on #[encoding(tags = "u8")]

[emturner]

Describe the bug
The useless-format clippy lint triggers when defining the tag size for an enum.

To Reproduce

#[derive(HasEncoding, NomReader, BinWriter)]
#[encoding(tags = "u8")]
enum Example {
  First,
  Second
}

Running cargo clippy -- --deny warnings results in:

error: useless use of `format!`
  --> <file>
   |
36 | #[encoding(tags = "u8")]
   |                   ^^^^ help: consider using `.to_string()`: `"u8".to_string()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format
   = note: `-D clippy::useless-format` implied by `-D warnings`

Expected behavior
The lint is not triggered