formats: load function takes combined manifest

Instead of having the pipeline and the source option as separate
arguments, the load function now takes the full manifest, which
has those two items combined.

test/mod/test_osbuild.py

@@ -30,8 +30,9 @@ class TestDescriptions(unittest.TestCase):
             {"build": None}
         ]
         for pipeline in cases:
+            manifest = {"pipeline": pipeline}
             with self.subTest(pipeline):
-                self.assertEqual(fmt.load(pipeline, {}).description(), {})
+                self.assertEqual(fmt.load(manifest).description(), {})
 
     def test_stage(self):
         name = "org.osbuild.test"