fix(deps): downgrade source_helper to <1.3.9 (SDK 3.8.0 compat)

Author: mfazrinizar

pubspec.yaml

@@ -16,7 +16,7 @@ dependencies:
   logging: ^1.3.0
   pointycastle: ^4.0.0
   source_gen: ^4.2.0
-  source_helper: ^1.3.10
+  source_helper: ">=1.3.4 <1.3.9"
 
 dev_dependencies:
   build_runner: ^2.11.1