[MC-257424] The name of the new default player heads is not capitalized

The name of the new default player heads is not capitalized.

Reproduce:

Old default role name using capitalization. MHF_Alex's Head

/give @p player_head{SkullOwner:MHF_Alex}

The name of the new default player heads is not capitalized. mhf_zuri's Head

/give @p player_head{SkullOwner:MHF_Zuri}

This is inconsistent with the names of all the previous heads.