PostgreSQL: Pin canonical rendering of no-space prefix @

tests/sqlparser_postgres.rs

diff --git a/tests/sqlparser_postgres.rs b/tests/sqlparser_postgres.rs
index 14f845f..c85cb26 100644
--- a/tests/sqlparser_postgres.rs
+++ b/tests/sqlparser_postgres.rs
@@ -9959,6 +9959,7 @@
     // `@-` tokenizes as a geometric operator prefix, so displaying PGAbs
     // without a space breaks re-parsing of a negative operand.
     pg().verified_stmt("SELECT @ -2");
+    pg().one_statement_parses_to("SELECT @a", "SELECT @ a");
     let err = pg().parse_sql_statements("SELECT @-2").unwrap_err();
     assert_eq!(
         ParserError::TokenizerError(