test_list_tahoe_objects failure

[meejah]

Under tahoe-lafs 1.19 and master the integration test _tahoe_list_objects fails by producing one (of the twenty) metadata objects "too big".

I'm not sure what's going on here, and will file a tahoe-lafs ticket as well.

The magic-folder API returns this (after creating 20x identical folders with a single Snapshot):

    # [                                                                                                                 
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 190],                                                                                              
    #     [416, 800, 292]                                                                                               
    # ]                                                                                                                 

They should all be identical, but the last one as a 292 byte metadata, instead of 190-byte metadata. This works fine on tahoe-lafs 1.17 and 1.18