sqlx-postgres: fix correct operator precedence in byte length check

[cuiweixie]

Does your PR solve an issue?

Is this a breaking change?

no

If yes, this pull request will need to wait for the next major release (0.{x + 1}.0)

Behavior changes can be breaking if significant enough.
Consider Hyrum's Law:

With a sufficient number of users of an API,
it does not matter what you promise in the contract:
all observable behaviors of your system
will be depended on by somebody.

[cuiweixie]

this ci failed is:

error[E0599]: no method named `parse2` found for struct `Pkcs12` in the current scope
   --> /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/native-tls-0.2.12/src/imp/openssl.rs:162:29
    |
162 |         let parsed = pkcs12.parse2(pass)?;
    |                             ^^^^^^
    |
help: there is a method `parse` with a similar name
    |
162 -         let parsed = pkcs12.parse2(pass)?;
162 +         let parsed = pkcs12.parse(pass)?;
    |

For more information about this error, try `rustc --explain E0599`.

it seems is unrelated to this pr.