Simplify Woodpecker pipeline by consolidating when conditions and using secrets for Fly.io authentication

.woodpecker.yml

@@ -1,27 +1,23 @@
-when:
-  branch:
-    - main
-  event:
-    - push
-
 steps:
   deploy_frontend:
     image: node:20
-    environment:
-      FLY_API_TOKEN:
-        from_secret: FLY_API_TOKEN
+    secrets: [FLY_API_TOKEN]
     commands:
       - curl -L https://fly.io/install.sh | sh
       - export PATH="$HOME/.fly/bin:$PATH"
       - flyctl deploy --config fly.toml --app gallus-pub --remote-only
+    when:
+      branch: main
+      event: push
 
   deploy_backend:
     image: node:20
-    environment:
-      FLY_API_TOKEN:
-        from_secret: FLY_API_TOKEN
+    secrets: [FLY_API_TOKEN]
     commands:
       - cd backend
       - curl -L https://fly.io/install.sh | sh
       - export PATH="$HOME/.fly/bin:$PATH"
       - flyctl deploy --config fly.toml --app gallus-cms-backend --remote-only
+    when:
+      branch: main
+      event: push