fix feature_advanced_keycodes.md's link (#7421)

fix feature_advanced_keycodes.md's link (#7421)

docs/feature_advanced_keycodes.md has:
```
[Tap Dance](https://github.com/qmk/qmk_firmware/blob/master/docs/feature_tap_dance.md#example-5-using-tap-dance-for-advanced-mod-tap-and-layer-tap-keys)
```

change to:
```
[Tap Dance](feature_tap_dance.md#example-5-using-tap-dance-for-advanced-mod-tap-and-layer-tap-keys)
```