Update `update-dev.yml` to use `git` instead of third-party action

[mudit2812]

The update-dev action keeps failing due to unrelated histories between the dev and master branches, and the third party action used for the nightly merge does not include any options to allow merging with unrelated histories. So, this PR updates the action to use git instead.

This will also give us more flexibility in the future.

Couple of updates:

• I have confirmed that configuring git using secrets.NIGHTLY_TOKEN does not expose the token in the workflow logs. See here for an example.

[sc-76254]