use fill_value = 0 in metadata consolidation test

Author: d-v-b

tests/test_metadata/test_consolidated.py

@@ -522,7 +522,7 @@ async def test_consolidated_metadata_v2(self):
                         dtype=dtype,
                         attributes={"key": "a"},
                         chunks=(1,),
-                        fill_value=None,
+                        fill_value=0,
                         compressor=Blosc(),
                         order="C",
                     ),