chore: fix spanner_postgres_create_database region tag

[bshaffer]

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[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• spanner/src/pg_create_database.php:26, tag spanner_postgresql_create_database

You are about to delete 1 region tag.

• spanner/src/pg_create_database.php:26, tag spanner_create_postgres_database

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