Allow the latest vm service (#1718)

Allow the latest vm_service in test_core.

Fixes #1717
diff --git a/pkgs/test_core/pubspec.yaml b/pkgs/test_core/pubspec.yaml
index 24dae0d..b96cc06 100644
--- a/pkgs/test_core/pubspec.yaml
+++ b/pkgs/test_core/pubspec.yaml
@@ -25,7 +25,7 @@
   source_span: ^1.8.0
   stack_trace: ^1.10.0
   stream_channel: ^2.1.0
-  vm_service: ">=6.0.0 <9.0.0"
+  vm_service: ">=6.0.0 <10.0.0"
   yaml: ^3.0.0
   # matcher is tightly constrained by test_api
   matcher: any