depth: Change Black's 5th step depth from 3 to 5

```
 1.    d2    b4
 2.    f4    d6
 3.    d7    g4
 4.    a7    g7
 5.    g1    e4
```

===> E4 is bad,and d5/e5/e4/e3 is bad.

Level 3 sometimes is bad.

Leve 5 is ok!!!

level 18 + block path can solve.

level 15 + block path sometimes cannot solve.

```
 1.    f4    d2
 2.    d6    b4
 3.    d3    g4
 4.    a4    d1
 5.    g7    c4
```

===> C4 is bad move （45）

Level 3 Open mobility can fix. no issue.

And c4/a7/e3/g1 is bad.

level 5 is ok.

level  18 + block path cannot solve.

level 15 sometimes cannot solve.

```
Black:
Bad move: f6
Good move: c5 / b4 / b2 / d3 / d2 / e3
F6/a7/b6/a4/a1/c3/f2/e5/g1 is bad

 1.     d1    d6
 2.     c4    f4
 3.     g7    d7
 4.     d5    g4
 5.     e4

1 OK
3 OK
5 Leve 5 is not ok, sometimes is e5, if block path is on, level 5 is ok, so need to enable it by default?
7 X
10 X
11 X
12 X
15 X
17 X
18 X

And also can fit

(Commit ff37bc3)

Black:
Bad move: d5
Good move: f2xd7

 1.     d6    f4
 2.     b4    d2
 3.     b6    f6
 4.     b2xf6    f6
 5.     d7

1 half X
2 OK
3 X
5 X
```

```
 1.     b4    f4
 2.     d6    d2
 3.     b6    f6
 4.     b2xf6    f6
 5.     c5    f2xd6
```

(bad 39)

```
Good:  f2xc5/ or no mill

1 OK
2 X
3 OK
4 X
5 OK
6 X
7 OK
8 X
9 X
10 OK
11 OK
12 OK
13 X
14 X
15 OK
16 1/3 X
17 OK
18 OK
19 X
20
```

src/mills.cpp

@@ -484,7 +484,7 @@ Depth get_search_depth(const Position *pos)
             constexpr Depth placingDepthTable9[25] = {
                 +1,  1, +1,  1,  /* 0 ~ 3 */
                 +3,  3, +3,  15, /* 4 ~ 7 */
-                +15, 3, +18, 0,  /* 8 ~ 11 */
+                +15, 5, +18, 0,  /* 8 ~ 11 */
                 +0,  0, +0,  0,  /* 12 ~ 15 */
                 +0,  0, +0,  0,  /* 16 ~ 19 */
                 +0,  0, +0,  0,  /* 20 ~ 23 */