ci: fix Woodpecker v3 secret syntax (use environment + from_secret)

.woodpecker.yml

@@ -21,9 +21,11 @@ steps:
 
   deploy:
     image: bitnami/kubectl:latest
+    environment:
+      KUBECONFIG_DATA:
+        from_secret: kubeconfig
     commands:
-      - mkdir -p ~/.kube && echo "$KUBECONFIG" > ~/.kube/config
+      - mkdir -p ~/.kube && echo "$KUBECONFIG_DATA" > ~/.kube/config
       - kubectl set image deployment/stemedb-api stemedb-api=registry.threesix.ai/stemedb-api:${CI_COMMIT_SHA:0:8} -n stemedb
       - kubectl rollout status deployment/stemedb-api -n stemedb --timeout=300s
-    secrets: [kubeconfig]
     depends_on: [build]