Bump test from 1.21.5 to 1.21.6 in /device_doctor (#2119)

diff --git a/device_doctor/pubspec.lock b/device_doctor/pubspec.lock
index ec4fdd4..0b308df 100644
--- a/device_doctor/pubspec.lock
+++ b/device_doctor/pubspec.lock
@@ -420,21 +420,21 @@
       name: test
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.21.5"
+    version: "1.21.6"
   test_api:
     dependency: transitive
     description:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.4.13"
+    version: "0.4.14"
   test_core:
     dependency: transitive
     description:
       name: test_core
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.4.17"
+    version: "0.4.18"
   timing:
     dependency: transitive
     description:
@@ -485,4 +485,4 @@
     source: hosted
     version: "3.1.1"
 sdks:
-  dart: ">=2.18.0-146.0.dev <3.0.0"
+  dart: ">=2.18.0 <3.0.0"