[submodule] Update submodule sonic-mgmt-common to the latest HEAD aut…

…omatically (#19845)

#### Why I did it
src/sonic-mgmt-common
```
* 966adc0 - (HEAD -> master, origin/master, origin/HEAD) Fix sonic-net/sonic-gnmi#266 (#143) (4 hours ago) [Steve Licking]
```
#### How I did it
#### How to verify it
#### Description for the changelog