GH Action: Cryptographically sign commits

Signed-off-by: Ole Herman Schumacher Elgesem <ole.elgesem@northern.tech>

Author: olehermanse

.github/workflows/format.yml

@@ -46,7 +46,7 @@ jobs:
           git config user.email '<noreply@github.com>'
           shopt -s globstar
           git add src/cfengine_cli/*.py src/cfengine_cli/**/*.py tests/*.py tests/**/*.py
-          git commit -F commit_message.txt
+          git commit -S -F commit_message.txt
       - id: commit-message-from-file
         name: Parse commit message from file into variable
         if: hashFiles('git_diff_exists') != ''