sqlparser: enforce bare * restriction in grammar (#19585)

Signed-off-by: Arthur Schreiber <arthur@planetscale.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: arthurschreiber

go/vt/sqlparser/parse_test.go

@@ -6635,10 +6635,10 @@ var invalidSQL = []struct {
 	output: "syntax error at position 39",
 }, {
 	input:  "select a, * from t",
-	output: "syntax error: unexpected '*' at position 12",
+	output: "syntax error at position 12",
 }, {
 	input:  "select *, * from t",
-	output: "syntax error: unexpected '*' at position 12",
+	output: "syntax error at position 12",
 }}
 
 func TestErrors(t *testing.T) {