Add signoff to Upmerge docs to edge workflow

[willdavsmith]

The Upmerge docs to edge workflow does not include a signoff message in the commit:

docs/.github/workflows/upmerge.yaml

Line 66 in 7ed3cea

git merge -m "Upmerge to edge" origin/$SOURCE_BRANCH

This causes DCO to fail during the release process. We should add a signoff flag to the git merge command.

AB#13660

[ytimocin]

Closing this now @willdavsmith. You can re-open if it is not fixed already.

[kachawla]

This hasn't been fixed yet, re-opening and removing triage label.

[ytimocin]

Needs to be worked on. The commit that added the sign-off was removed.

[brooke-hamilton]

/assign