cabal check doesn't detect using invalid version syntax for spec versions prior to 1.24

[hvr]

This already caused 4 incidents in the package index (see haskell-infra/hackage-trustees#128)

@phadej found the culprit at 6b3457d which relaxed the Version parser to accommodate parsing pkg-config output (which imho deserves its own version parsing anyway), and as an overlooked side-effect also relaxed the parsing of the cabal format.

[23Skidoo]

+1 on having a PkgConfigVersion type.