Set the number of shards for telemetry_unittest on Windows & Mac to be 2

testing/buildbot/chromium.fyi.json

Index: testing/buildbot/chromium.fyi.json
diff --git a/testing/buildbot/chromium.fyi.json b/testing/buildbot/chromium.fyi.json
index 740fa014dd9744ae8ca5b3b151a7f2c05f3901b0..dc0dfaea254f5a6a49abeee63836aeb5b14b5244 100644
--- a/testing/buildbot/chromium.fyi.json
+++ b/testing/buildbot/chromium.fyi.json
@@ -1993,7 +1993,8 @@
           "telemetry_unittests_run"
         ],
         "swarming": {
-          "can_use_on_swarming_builders": false
+          "can_use_on_swarming_builders": false,
+          "shards": 2
         }
       }
     ]
@@ -4479,7 +4480,8 @@
           "telemetry_unittests_run"
         ],
         "swarming": {
-          "can_use_on_swarming_builders": true
+          "can_use_on_swarming_builders": true,
+          "shards": 2
         }
       }
     ],