Fix spec-ver lower-bound for some 3.0 fields in cabal check

These are only supported properly starting with
cabal-version:3.0 (which has been enforced by
Hackage as well -- via this very patch).

See #6033 for details

Author: hvr

Cabal/Distribution/PackageDescription/Check.hs

@@ -1261,7 +1261,7 @@ checkCabalVersion pkg =
            [ display (Dependency name (eliminateMajorBoundSyntax versionRange))
            | Dependency name versionRange <- depsUsingMajorBoundSyntax ]
 
-  , checkVersion [2,1] (any (not . null)
+  , checkVersion [3,0] (any (not . null)
                         (concatMap buildInfoField
                          [ asmSources
                          , cmmSources
@@ -1270,7 +1270,7 @@ checkCabalVersion pkg =
       PackageDistInexcusable $
            "The use of 'asm-sources', 'cmm-sources', 'extra-bundled-libraries' "
         ++ " and 'extra-library-flavours' requires the package "
-        ++ " to specify at least 'cabal-version: >= 2.1'."
+        ++ " to specify at least 'cabal-version: 3.0'."
 
   , checkVersion [2,1] (any (not . null)
                         (buildInfoField virtualModules)) $