[infra] Increase the number of shards for dart2wasm to 30

Change-Id: I7e985e52d01f821db9c3626eac433e7352484217
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/235221
Reviewed-by: William Hesse <whesse@google.com>
diff --git a/tools/bots/test_matrix.json b/tools/bots/test_matrix.json
index 8280ab9..adbceae 100644
--- a/tools/bots/test_matrix.json
+++ b/tools/bots/test_matrix.json
@@ -2948,7 +2948,7 @@
             "language",
             "corelib"
           ],
-          "shards": 12,
+          "shards": 30,
           "fileset": "dart2wasm_hostasserts"
         }
       ]