Temporarily disable docs tests. (#111237)

This is to reopen the tree while jazzy installation is fixed.

Bug: https://github.com/flutter/flutter/issues/111193

.ci.yaml

@@ -242,6 +242,7 @@ targets:
       - master
     recipe: flutter/flutter
     presubmit: false
+    bringup: true # Marking as flaky to reopen the tree. https://github.com/flutter/flutter/issues/111193
     timeout: 60
     properties:
       dependencies: >-
@@ -258,6 +259,8 @@ targets:
 
   - name: Linux docs_test
     recipe: flutter/flutter
+    presubmit: false
+    bringup: true # Marking as flaky to reopen the tree. https://github.com/flutter/flutter/issues/111193
     timeout: 60
     properties:
       dependencies: >-