Disable synchronize_seqscans in 027_stream_regress.pl.
This script runs the core regression tests with quite a small value of
shared_buffers, making it prone to breakage due to synchronize_seqscans
kicking in where the tests don't expect that. Disable that feature to
stabilize the tests.
Discussion: https://postgr.es/m/
1258185.
1648876239@sss.pgh.pa.us