Note when `--enable-vmservice` is required and skip otherwise. (#167579)

Our CI system runs with `--enable-vmservice`, but the default (i.e. for
`flutter test`) does not.

Closes https://github.com/flutter/flutter/issues/136079.
https://dart.googlesource.com/external/github.com/flutter/flutter/+/b94e21b4390cd720d7cec05e22a732335a1e9cc9

DEPS

diff --git a/DEPS b/DEPS
index 70a892d..8426485 100644
--- a/DEPS
+++ b/DEPS
@@ -240,7 +240,7 @@
 deps = {
   'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '1d8f02efc19c8d4b1b3d08e6a56540f9d350d9e9',
 
-  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '731d2d9e779833c056419783465a37ceefe246a5',
+  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + 'b94e21b4390cd720d7cec05e22a732335a1e9cc9',
 
   'flutter/engine/src/flutter/third_party/depot_tools':
   Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + '580b4ff3f5cd0dcaa2eacda28cefe0f45320e8f7',

commits.json

diff --git a/commits.json b/commits.json
index 43f45db..9405ed6 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
-  "flutter":"731d2d9e779833c056419783465a37ceefe246a5",
+  "flutter":"b94e21b4390cd720d7cec05e22a732335a1e9cc9",
   "flutter/engine/src/flutter/third_party/dart":"1d8f02efc19c8d4b1b3d08e6a56540f9d350d9e9"
 }
\ No newline at end of file