Mark subprocess_test flaky

Not going to take the time to figure out the flakiness right now.

Change-Id: I48bd677d6c41091dc8554e6a9f9c3a344ec10c1d
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/aos/starter/BUILD b/aos/starter/BUILD
index e6dad81..2186421 100644
--- a/aos/starter/BUILD
+++ b/aos/starter/BUILD
@@ -77,6 +77,7 @@
     data = [
         "//aos/events:pingpong_config",
     ],
+    flaky = True,
     # The roborio compiler doesn't support <filesystem>.
     target_compatible_with =
         ["@platforms//os:linux"],