Else this will stall operations waiting for ProcSignalBarriers and may
cause pile-ups due to that. Since WAL archiving can take a while, this
helps in cases like DROP DATABASE where we require all backends to
release their file handles.

Note that the windows version should still do about the same as before,
but my windows days are long over, so take that code with a grain of
salt. It did pass CI though.

Suggested-by: Ronan Dunklau <ronan.dunklau@aiven.io>