pgsql: Use int64 for number of entries in pg_stat_statements

Use int64 for number of entries in pg_stat_statements

Commit 13b935cd changed hash_get_num_entries to return int64 instead
of long. This fixes a few more users of hash_get_num_entries which
were missed in the original commit.

PGSS_FILE_HEADER is left unchanged since this only affects as of yet
unreleased versions of PostgreSQL. Backpatch to v19 where the int64
change was performed.

Author: Karina Litskevich <litskevichkarina(at)gmail(dot)com>
Reviewed-by: Daniel Gustafsson <daniel(at)yesql(dot)se>
Discussion: https://postgr.es/m/CACiT8iYTkc33YWaA2D3t51Y5s=GqBO7T1zX7bkpSmet2njcLLw@mail.gmail.com
Backpatch-through: 19

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/de73e691e7f53a4fe08f09928a9f72331476a439

Modified Files
--------------
contrib/pg_stat_statements/pg_stat_statements.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)