pgsql: injection_points: Tweak more permutation in isolation test "basi

injection_points: Tweak more permutation in isolation test "basic"

The CI has reported that using a marker to force the output of the
detach step to happen after the wait step was not enough, as
isolationtester has managed to report the detach step as waiting before
the wait step finishes in some runs.

src/test/isolation/README tells that there is a more drastic method to
enforce the ordering of the output: an empty step positioned just after
the wait step can force the wait step to complete before the detach step
begins. This method has been able to pass 10 runs in the CI here, while
HEAD seems to fail 15~20% of the time in the CF bot.

Discussion: https://postgr.es/m/Z6WO8FbqK_FHmrzC@paquier.xyz

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/926c7fce03603b49dd2529e37d47b805730584fc

Modified Files
--------------
src/test/modules/injection_points/expected/basic.out | 3 ++-
src/test/modules/injection_points/specs/basic.spec | 7 ++++---
2 files changed, 6 insertions(+), 4 deletions(-)