Bump openhands-secrets chart to 0.1.18

The openhands-secrets chart was bumped to 0.1.17 in #649, but #650 had already
taken it to 0.1.17 on main first, so the two collided. The version-validation
job failed on the #649 merge (changes present, version not bumped vs base), and
the chart did not publish. Bumping to 0.1.18 publishes the bot-token secret
change under a fresh version and turns the main check green.

Author: ak684

charts/openhands-secrets/Chart.yaml

@@ -2,5 +2,5 @@ apiVersion: v2
 name: openhands-secrets
 description: A Helm chart for OpenHands secrets
 type: application
-version: 0.1.17
+version: 0.1.18
 appVersion: "1.0"