[submodule] Update submodule sonic-gnmi to the latest HEAD automatica…

…lly (#21231)

#### Why I did it
src/sonic-gnmi
```
* c6f36b9 - (HEAD -> master, origin/master, origin/HEAD) Merge pull request #331 from hdwhdw/test (27 hours ago) [Dawei Huang]
* 6bc20a0 - remove --debug from sed. (3 days ago) [Dawei Huang]
* 8427ba7 - follow the azure pipeline way. (3 days ago) [Dawei Huang]
* 657691c - update comment. (3 days ago) [Dawei Huang]
* 44fbc97 - no semgrep instead of nosem. (3 days ago) [Dawei Huang]
* c2aead9 - bypass semgrep check after auditing. (3 days ago) [Dawei Huang]
* 33db80a - sed debug mode. (3 days ago) [Dawei Huang]
* ff18bcd - use the CI sed hack to go can find the path of sonic-mgmt-common. (3 days ago) [Dawei Huang]
* e8bc547 - update documentation. (3 days ago) [Dawei Huang]
* 659e12d - change the clone path to address file not found issue. (3 days ago) [Dawei Huang]
* ebb7f3c - update to github pr target branch. (3 days ago) [Dawei Huang]
* fb263a9 - update ref to be the same as build branch. (3 days ago) [Dawei Huang]
* 19e941a - add ref to checkout (4 days ago) [Dawei Huang]
* 02d8dd1 - update to prevent deleting old repo. (4 days ago) [Dawei Huang]
* ad61814 - fix wrong url for repo. (4 days ago) [Dawei Huang]
* 66fdd2c - path needs to be under working dir. (4 days ago) [Dawei Huang]
* b91e3c6 - add checking out sonic-mgmt-common. (4 days ago) [Dawei Huang]
```
#### How I did it
#### How to verify it
#### Description for the changelog