Update dependency dart to ^3.9.3

.drone.yml

@@ -12,7 +12,7 @@ steps:
 
 # Frontend
 - name: web_build
-  image: node:24
+  image: node:23
   depends_on:
   - fetch
   volumes:

moneymgr_mobile/pubspec.yaml

@@ -19,7 +19,7 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 version: 1.0.0+1
 
 environment:
-  sdk: ^3.8.1
+  sdk: ^3.9.3
 
 # Dependencies specify other packages that your package needs in order to work.
 # To automatically upgrade your package dependencies to the latest versions