pgsql: Attempt to fix unstable regression tests, take 2

Attempt to fix unstable regression tests, take 2

Following up on 2dc16efed, petalura has suffered some additional
failures in stats_ext which again appear to be around the timing of an
autovacuum during the test, causing instability in the row estimates.

Again, let's fix this by explicitly performing a VACUUM on the table
and not leave it to happen by chance of an autovacuum pass.

Discussion: https://postgr.es/m/CAApHDvok5hmXr%2BbUbJe7%2B2sQzWo4B_QzSk7RKFR9fP6BjYXx5g%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/24566b359d095c3800c2a326d88a595722813f58

Modified Files
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src/test/regress/expected/stats_ext.out | 10 +++++-----
src/test/regress/sql/stats_ext.sql      | 10 +++++-----
2 files changed, 10 insertions(+), 10 deletions(-)