fix alignment of emit_unbox_store copy (#52505)
The dest alignment might be determined to be greater than the source.
For example, observed with:
code_llvm(dump_module=true, optimize=false, (Int,)) do x
Pair(ntuple(i -> 0x00, 8), x)
end
Where the alignment of the first field of the Pair is at least 4, but
the alignment of the ntuple data is 1.
(discovered while analyzing an ARM build failure @staticfloat)
