pgsql: pg_stat_statements: Add test coverage for pg_stat_statements_1_8

pg_stat_statements: Add test coverage for pg_stat_statements_1_8()

This requires reading pg_stat_statements at least once while the 1.8
version of the extension is installed.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/40d1e4f2-835f-448f-a541-8ff5db75bf3d@eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3727b8d0e3f1fa7568f6a6f4378ce5a79daeb0d9

Modified Files
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.../pg_stat_statements/expected/oldextversions.out | 24 ++++++++++++++--------
contrib/pg_stat_statements/sql/oldextversions.sql  |  3 ++-
2 files changed, 17 insertions(+), 10 deletions(-)