fix(deps): update dependency build to v4

Author: renovate[bot]

pubspec.yaml

@@ -9,7 +9,7 @@ environment:
   sdk: '>=2.7.0 <3.0.0'
 
 dependencies:
-  build: ^2.3.0
+  build: ^4.0.0
   source_gen: ^1.2.2
   analyzer: ^4.1.0
   mustache: ^1.1.1