Allow package to be listed twice in cabal.project (#9449)

This makes `checkTarget` a little smarter by deduplicating the
`TargetPackage` so as not to error out when the user has the line

    package: .

twice in their `cabal.project`.

Fixes #9448

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

cabal-install/src/Distribution/Client/ProjectOrchestration.hs

@@ -3,6 +3,7 @@
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE ViewPatterns #-}
 
 -- | This module deals with building and incrementally rebuilding a collection
 -- of packages. It is what backs the @cabal build@ and @configure@ commands,
@@ -642,7 +643,7 @@ resolveTargets
       checkTarget :: TargetSelector -> Either (TargetProblem err) [(UnitId, ComponentTarget)]
 
       -- We can ask to build any whole package, project-local or a dependency
-      checkTarget bt@(TargetPackage _ [pkgid] mkfilter)
+      checkTarget bt@(TargetPackage _ (ordNub -> [pkgid]) mkfilter)
         | Just ats <-
             fmap (maybe id filterTargetsKind mkfilter) $
               Map.lookup pkgid availableTargetsByPackageId =