[ios] Rolls the ios-webkit-tot bot to Xcode 11.3.1 (11C505).

CIPD packages:
  infra_internal/ios/xcode/mac  11c505wk
  infra_internal/ios/xcode/ios  11c505wk

BUG=None

Change-Id: I8b4f9670e22f259877eb7e99e6c76846628d6eec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2059056Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742187}

ios/build/bots/chromium.fyi/ios-webkit-tot.json

@@ -2,7 +2,7 @@
   "comments": [
     "Run tests against ToT webkit."
   ],
-  "xcode build version": "11a1027wk",
+  "xcode build version": "11c505wk",
   "gn_args": [
     "goma_dir=\"$(goma_dir)\"",
     "is_component_build=false",