.github/actions: add signoff to go-licenses commits

also set git committer, which is apparently what this action uses for
signoff rather than git author.  Remove branch-suffix, which isn't
proving useful, and add installation_id, which isn't technically
necessary in the tailscale/tailscale repo, but makes this consistent
with the workflows in other repos.

Signed-off-by: Will Norris <will@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f