Closes #2719 by bumping bigdecimal version

[FaveroFerreira]

This PR bumps the bigdecimal version to enable using the latest bigdecimal crate version solving #2719.

[dnlsndr]

@abonader Is this blocked by somethig, or would it be possible to merge this? This is especially problematic, as a project might utilize bigdecimal and depends on version 0.4.x of that crate. Having two different versions of that crate in your project can lead to further problems down the road (importing from the wrong crate, incompatability of the different versions), so it would be really nice if we had a common BigDecimal version or at least a up-to-date version, that a project could re-use without requiring its own BigDecimal version.

[mplanchard]

This would also be useful since BigDecimal has implemented From impls for u128 and i128 in the 0.4 series, so while e.g. 12_u128.into() works for our normal use of BigDecimal, it fails using sqlx::types::BigDecimal