Carved pumpkin has to be explicitly registered as a separate node, as
registering a carved pumpkin node happened as a side effect of invoking
mcl_farming:add_gourd() for the carved pumpkin.
The iron / snow golem spawning checks that trigger whenever a carved
pumpkin is placed had to be moved out of the mcl_farming:add_gourd()
invocation to preserve the existing behaviour.
Note that uncarved pumpkin must not be registered as a separate node,
as invoking mcl_farming:add_gourd() for a registered node name leads to
stems not updating when an adjacent node is manually placed or mined.
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