roachtest: fix schema change statement in mixed version test

The test was executing a schema change statement that doesn't succeed,
since ON UPDATE expressions can't reference other columns.

Release note: None

Author: rafiss

pkg/cmd/roachtest/tests/mixed_version_job_compatibility_in_declarative_schema_changer.go

@@ -118,7 +118,7 @@ func executeSupportedDDLs(
 		`TRUNCATE testdb.testsc.t3`,
 		`ALTER TABLE testdb.testsc.t2 RENAME TO t2_renamed`,
 		`ALTER TABLE testdb.testsc.t2_renamed RENAME TO t2`,
-		`ALTER TABLE testdb.testsc.t2 ALTER COLUMN j SET ON UPDATE j + 1`,
+		`ALTER TABLE testdb.testsc.t2 ALTER COLUMN j SET ON UPDATE 1`,
 		`ALTER TABLE testdb.testsc.t2 RENAME COLUMN k TO k_renamed`,
 		`ALTER TABLE testdb.testsc.t2 RENAME COLUMN k_renamed TO k`,
 	}