Updated sqlx version, and also applied a couple of minor fixes.

[arshadm]

I am working on a production app which is using sqlb, we use both postgres and sqlite. Unfortunately, upgrading to sqlx 0.8.0 caused a dependency issue with sqlb as it is on 0.7.x and the sqlite dependencies are incompatible.

I have update the sqlx dependency, and also fixed a compilation issue due to a missing feature which the latest version of cargo picked up.

I also modified the tests to pickup the database URL from the environment variable DATABASE_URL (the existing value is used as fallback). This is the same variable that the sqlx macros use.