Update min Swift version to 5.6 and make platform versions consistent

[codecov-commenter]

Codecov Report

Merging #763 (b5bf21c) into main (8d60150) will decrease coverage by 0.19%. The diff coverage is n/a.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #763 +/- ## ========================================== - Coverage 61.01% 60.82% -0.19% ========================================== Files 15 15 Lines 531 531 ========================================== - Hits 324 323 -1 - Misses 207 208 +1 ``` [see 1 file with indirect coverage changes](https://codecov.io/gh/vapor/fluent/pull/763/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 4.8.0