internal/pkg: do not discard the result of compact

This result was mistakenly unused resulting in incorrect identifiers for artifacts with duplicate dependencies.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg.go

@@ -314,7 +314,7 @@ func (k Kind) Ident(params []byte, deps ...Artifact) ID {
 	slices.SortFunc(identifiers, func(a, b extIdent) int {
 		return bytes.Compare(a[:], b[:])
 	})
-	slices.Compact(identifiers)
+	identifiers = slices.Compact(identifiers)
 
 	h := sha512.New384()
 	h.Write(binary.LittleEndian.AppendUint64(nil, uint64(k)))