Fix new compact block allocation in allocateForCompact
allocateForCompact() is called when nursery of a compact region is full, to add new blocks to the compact. New blocks added to an existing region needs a StgCompactNFDataBlock header, not a StgCompactNFData.
This fixes allocateForCompact() so that it now correctly allocates space for StgCompactNFDataBlock instead of StgCompactNFData as before.
Fixes #17044 (closed).
A regression test T17044 added.