pgsql: Add NOT NULL checking of pg_stat_statements_reset() in tests

Add NOT NULL checking of pg_stat_statements_reset() in tests

This is preliminary patch.  It adds NOT NULL checking for the result of
pg_stat_statements_reset() function. It is needed for upcoming patch
"Track statement entry timestamp" that will change the result type of
this function to the timestamp of a reset performed.

Discussion: https://postgr.es/m/flat/72e80e7b160a6eb189df9ef6f068cce3765d37f8.camel%40moonset.ru
Author: Andrei Zubkov
Reviewed-by: Julien Rouhaud, Hayato Kuroda, Yuki Seino, Chengxi Sun
Reviewed-by: Anton Melnikov, Darren Rush, Michael Paquier, Sergei Kornilov
Reviewed-by: Alena Rybakina, Andrei Lepikhov

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6ab1dbd26bbf307055d805feaaca16dc3e750d36

Modified Files
--------------
contrib/pg_stat_statements/expected/cursors.out    |  28 ++--
contrib/pg_stat_statements/expected/dml.out        |  28 ++--
.../pg_stat_statements/expected/level_tracking.out | 112 ++++++-------
contrib/pg_stat_statements/expected/planning.out   |  18 +--
contrib/pg_stat_statements/expected/select.out     |  44 ++---
.../pg_stat_statements/expected/user_activity.out  | 120 +++++++-------
contrib/pg_stat_statements/expected/utility.out    | 178 ++++++++++-----------
contrib/pg_stat_statements/expected/wal.out        |  10 +-
contrib/pg_stat_statements/sql/cursors.sql         |   6 +-
contrib/pg_stat_statements/sql/dml.sql             |   6 +-
contrib/pg_stat_statements/sql/level_tracking.sql  |  16 +-
contrib/pg_stat_statements/sql/planning.sql        |   4 +-
contrib/pg_stat_statements/sql/select.sql          |  10 +-
contrib/pg_stat_statements/sql/user_activity.sql   |  15 +-
contrib/pg_stat_statements/sql/utility.sql         |  32 ++--
contrib/pg_stat_statements/sql/wal.sql             |   2 +-
16 files changed, 317 insertions(+), 312 deletions(-)