Update min Swift version to 5.6 and make platform versions consistent

[codecov-commenter]

Codecov Report

Merging #165 (7e69f46) into main (0bfb5d5) will increase coverage by 0.13%. The diff coverage is n/a.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #165 +/- ## ========================================== + Coverage 69.27% 69.41% +0.13% ========================================== Files 94 94 Lines 3486 3495 +9 ========================================== + Hits 2415 2426 +11 + Misses 1071 1069 -2 ``` | [Impacted Files](https://codecov.io/gh/vapor/sql-kit/pull/165?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [...s/SQLKit/Concurrency/SQLDatabase+Concurrency.swift](https://codecov.io/gh/vapor/sql-kit/pull/165?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQ29uY3VycmVuY3kvU1FMRGF0YWJhc2UrQ29uY3VycmVuY3kuc3dpZnQ=) | `0.00% <ø> (ø)` | | | [...LKit/Concurrency/SQLQueryBuilder+Concurrency.swift](https://codecov.io/gh/vapor/sql-kit/pull/165?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQ29uY3VycmVuY3kvU1FMUXVlcnlCdWlsZGVyK0NvbmN1cnJlbmN5LnN3aWZ0) | `100.00% <ø> (ø)` | | | [...LKit/Concurrency/SQLQueryFetcher+Concurrency.swift](https://codecov.io/gh/vapor/sql-kit/pull/165?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQ29uY3VycmVuY3kvU1FMUXVlcnlGZXRjaGVyK0NvbmN1cnJlbmN5LnN3aWZ0) | `33.33% <ø> (ø)` | | ... and [8 files with indirect coverage changes](https://codecov.io/gh/vapor/sql-kit/pull/165/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor)

[VaporBot]

These changes are now available in 3.25.0