Allow the latest package:analyzer

Closes #681

PiperOrigin-RevId: 553733481

Author: natebosch

CHANGELOG.md

@@ -1,6 +1,6 @@
 ## 5.4.3-wip
 
-* Require analyzer 5.12.0.
+* Require analyzer 5.12.0, allow analyzer version 6.x;
 * Add example of writing a class to mock function objects.
 
 ## 5.4.2

pubspec.yaml

@@ -9,7 +9,7 @@ environment:
   sdk: '>=2.19.0 <4.0.0'
 
 dependencies:
-  analyzer: '>=5.12.0 <6.0.0'
+  analyzer: '>=5.12.0 <7.0.0'
   build: '>=1.3.0 <3.0.0'
   code_builder: ^4.5.0
   collection: ^1.15.0