imagebuilder: accept manifest_type

The `imagebuilder` phase was missing the `manifest_type` property in its
schema. While pungi (often) guesses correctly for the `manifest_type` it
doesn't do so in the case of ostree installer images; thus it needs to
be allowed.

This was an oversight as the phase implementation already looked for
this value in the configuration.

Signed-off-by: Simon de Vlieger <supakeen@redhat.com>
(cherry picked from commit 0ade83b0e9adc43b4e9fd38d536d647f42126688)

pungi/checks.py

@@ -1463,6 +1463,7 @@ def make_schema():
                                     "additionalProperties": True,
                                 },
                                 "seed": {"type": "integer"},
+                                "manifest_type": {"type": "string"},
                             },
                             "required": [
                                 "name",

tests/test_imagebuilderphase.py

@@ -61,6 +61,7 @@ class TestImageBuilderPhase(PungiTestCase):
                 "repos": ["https://example.com/repo/", "Client"],
                 "types": ["custom"],
                 "version": "Rawhide",
+                "manifest_type": "custom-type",
             },
         )
         compose = DummyCompose(self.topdir, {"imagebuilder": {"^Server$": [cfg]}})