generated default value column gets backticked when stored causing unable to insert to the table

Repro:
```
CREATE TABLE test_like_gen_1 (a int, b int GENERATED ALWAYS AS (a * 2) STORED);
INSERT INTO test_like_gen_1 (a) VALUES (1);
```
Err:
```Invalid default value for '(`a` * 2)': at or near "`":```