ci: scala steward DCO by hardcoding the message (#1074)

Signed-off-by: Yurii Shynbuiev <yurii.shynbuiev@iohk.io>

.scala-steward.conf

@@ -20,4 +20,9 @@ updates.ignore = [
 # If set, Scala Steward will only create or update `n` PRs each time it runs (see `pullRequests.frequency` above).
 # Useful if running frequently and/or CI build are costly
 # Default: null
-updates.limit = 5
+updates.limit = 5
+
+# If set, Scala Steward will use this message template for the commit messages and PR titles.
+# Supported variables: ${artifactName}, ${currentVersion}, ${nextVersion} and ${default}
+# Default: "${default}" which is equivalent to "Update ${artifactName} to ${nextVersion}"
+commits.message = "${default}\n\nSigned-off-by: Hyperledger Bot <hyperledger-bot@hyperledger.org>"