pgsql: Fix typo in error message

Fix typo in error message

Author: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: /messages/by-id/CAJTYsWXFy1j_T82+M_S9kFxU414tQYnZQD-b82=oL_LbG_5fPQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5778fb3eafd05c562af5d4585baf0e3ac57d07e0

Modified Files
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src/backend/commands/propgraphcmds.c | 2 +-
src/test/regress/expected/create_property_graph.out | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)