Fix the flutter run -d linux tests (flutter#120721)

* Fix the Linux run_debug_test_linux test

* ?

* Also do release

* ??

Author: loic-sharma

.ci.yaml

@@ -702,6 +702,7 @@ targets:
     bringup: true
     timeout: 60
     properties:
+      xvfb: "1"
       dependencies: >-
         [
           {"dependency": "clang", "version": "git_revision:5d5aba78dbbee75508f01bcaa69aedb2ab79065a"},
@@ -721,6 +722,7 @@ targets:
     recipe: devicelab/devicelab_drone
     timeout: 60
     properties:
+      xvfb: "1"
       dependencies: >-
         [
           {"dependency": "clang", "version": "git_revision:5d5aba78dbbee75508f01bcaa69aedb2ab79065a"},