distro: bring back TestImageType_PackageSetsChains()

This test was removed because package sets in chains are no longer
visible in the map returned from ImageType.PackageSets().
Bringing back the test now to ensure that:
1. All package set names defined in the keys returned from the
   PackageSets() map match the keys returned from the
   PackageSetsChains() map.
2. All package sets defined in the package set chains are defined for
   the image type.  This is tested by the function PackageSets()
   function itself, which should never panic.

internal/distro/distro_test.go

@@ -1,11 +1,14 @@
 package distro_test
 
 import (
+	"fmt"
 	"testing"
 
+	"github.com/osbuild/osbuild-composer/internal/blueprint"
 	"github.com/osbuild/osbuild-composer/internal/distro"
 	"github.com/osbuild/osbuild-composer/internal/distro/distro_test_common"
 	"github.com/osbuild/osbuild-composer/internal/distroregistry"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -99,3 +102,27 @@ func TestDistro_Version(t *testing.T) {
 		require.Error(err, "Invalid manifest did not return an error")
 	}
 }
+
+// Ensure that all package sets defined in the package set chains are defined for the image type
+func TestImageType_PackageSetsChains(t *testing.T) {
+	distros := distroregistry.NewDefault()
+	for _, distroName := range distros.List() {
+		d := distros.GetDistro(distroName)
+		for _, archName := range d.ListArches() {
+			arch, err := d.GetArch(archName)
+			require.Nil(t, err)
+			for _, imageTypeName := range arch.ListImageTypes() {
+				t.Run(fmt.Sprintf("%s/%s/%s", distroName, archName, imageTypeName), func(t *testing.T) {
+					imageType, err := arch.GetImageType(imageTypeName)
+					require.Nil(t, err)
+
+					imagePkgSets := imageType.PackageSets(blueprint.Blueprint{}, nil)
+					for packageSetName := range imageType.PackageSetsChains() {
+						_, ok := imagePkgSets[packageSetName]
+						assert.Truef(t, ok, "package set %q defined in a package set chain is not present in the image package sets", packageSetName)
+					}
+				})
+			}
+		}
+	}
+}