Generator: require source_gen 4.0.1 to not use APIs removed in analyzer 8.4

analyzer 8.4.0 again removed public API
(DartObjectImpl.getInvocation()) in a minor release, breaking source_gen
versions before 4.0.1.

Author: greenrobot-team

generator/pubspec.yaml

@@ -10,13 +10,13 @@ environment:
 
 dependencies:
   objectbox: 5.0.0
-  analyzer: '>=7.4.0 <9.0.0' # Allow version 8, but don't require it, yet (to use its API) for compat with more third-party packages
+  analyzer: '>=8.1.1 <9.0.0' # source_gen 4.0.1 requires at least 8.1.1
   build: ^3.0.0 # source_gen 3 requires 3.0.0
   collection: ^1.18.0 # Would require 1.19.1, but Flutter 3.24.0 has 1.18.0 pinned
   dart_style: '>=2.3.7 <4.0.0' # require 2.3.7 for languageVersion in DartFormatter constructor
   glob: ^2.1.3
   path: ^1.9.1
-  source_gen: ^3.1.0 # Require 3.1.0 to use new TypeChecker APIs
+  source_gen: ^4.0.1 # Require 4.0.1, older versions use APIs removed in analyzer 8.4.0
   pubspec_parse: ^1.4.0
   yaml: ^3.1.3
   http: ^1.3.0