Connection.setReadOnly(true) still allows DML statements to execute

Connection conn = ...;
conn.setReadOnly(true);
conn.createStatement().execute("INSERT INTO foo VALUES ('bar')");

Result: INSERT is executed
Expected: SQLException is thrown, no INSERT is executed

This bug plus CONJ-1306 mean that it's not possible to establish connections where the client is unable to execute DML statements. This is okay if the user can be limited to e.g. SELECT statements, but that's not always feasible.