Extend Liftoff mobile field trial to ios

The finch runs on all mobile platforms, so also the field trial should
run on both android and ios.

R=bcwhite@chromium.org

Bug: 1040061, 1040030
Change-Id: Ie4f46f66f3357f85fe8c771db3c5bf7392042353
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2030951Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737844}

testing/variations/fieldtrial_testing_config.json

@@ -7143,7 +7143,8 @@
     "V8WasmLiftoffMobile": [
         {
             "platforms": [
-                "android"
+                "android",
+                "ios"
             ],
             "experiments": [
                 {