Add dependency override for pkg:test (#477)

Because pkg:test does not allow pkg:http ^0.13.0

Author: kevmoo

pubspec.yaml

@@ -18,5 +18,7 @@ dev_dependencies:
   test: ^1.16.0-nullsafety.4
 
 dependency_overrides:
+  # Because pkg:test does not support pkg:http ^0.13.0
+  test: ^1.16.0-nullsafety.5
   http_parser:
     git: https://github.com/dart-lang/http_parser