prepend! allocates when X is empty even when there's capacity

[dpinol]

This does not report any allocation in julia 1.10, but reports 2 allocations in the first prepend! in julia 1.11rc4 & julia 1.12 master.
I guess it shouldn't allocate because x has enough capacity.

const x=Vector{Int}(undef, 1000)
empty!(x) 
@time prepend!(x, 10)
@time prepend!(x, 10)

0.000007 seconds (2 allocations: 16.844 KiB)
  0.000001 seconds

The same happens with insert!(x,1, 10), which is called twice by the first insertion into an SparseArray

[oscardssmith]

This is funny. The code was specifically designed not to do that, but a typo means that it always allocates rather that copy the data forward if there isn't enough space at the beginning of the array. Fix incoming.

[Moelf]

this is fixed in #56029.