ci: enable sign-off for auto commits [ci skip]

Signed-off-by: Khosrow <khos2ow@gmail.com>

Author: khos2ow

.github/workflows/update-tfdocs.yml

@@ -77,3 +77,4 @@ jobs:
           commit_user_name: terraform-docs-bot
           commit_user_email: bot@terraform-docs.io
           commit_author: "terraform-docs-bot <bot@terraform-docs.io>"
+          commit_options: "--signoff"