deflake the dartdocs test (#23582)

diff --git a/dev/devicelab/manifest.yaml b/dev/devicelab/manifest.yaml
index 58e1300..45a342bd 100644
--- a/dev/devicelab/manifest.yaml
+++ b/dev/devicelab/manifest.yaml
@@ -459,7 +459,6 @@
       Tracks how many members are still lacking documentation.
     stage: devicelab
     required_agent_capabilities: ["linux/android"]
-    flaky: true
 
   flutter_test_performance:
     description: >