[ios] fix ios14-beta xcode

ios14-beta-sim upstream is failing b/c of bad xcode value.

Change-Id: I1572a773f4ce33d76bb536cbe0c39f88e3340693
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2365294
Auto-Submit: Jeff Yoon <jeffyoon@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799874}

infra/config/generated/cr-buildbucket.cfg

@@ -10074,7 +10074,7 @@ buckets {
         cipd_version: "refs/heads/master"
         cmd: "recipes"
       }
-      properties: "{\"$build/goma\":{\"rpc_extra_params\":\"?prod\",\"server_host\":\"goma.chromium.org\"},\"$kitchen\":{\"devshell\":true,\"git_auth\":true},\"mastername\":\"chromium.fyi\",\"recipe\":\"chromium\",\"xcode_build_version\":\"x12a8179i_audio\"}"
+      properties: "{\"$build/goma\":{\"rpc_extra_params\":\"?prod\",\"server_host\":\"goma.chromium.org\"},\"$kitchen\":{\"devshell\":true,\"git_auth\":true},\"mastername\":\"chromium.fyi\",\"recipe\":\"chromium\",\"xcode_build_version\":\"12a8179i_audio\"}"
       execution_timeout_secs: 36000
       caches {
         name: "xcode_ios_12a8179i_audio"

infra/config/subprojects/chromium/master-only/ci.star

@@ -1900,7 +1900,7 @@ ci.fyi_ios_builder(
     executable = "recipe:chromium",
     os = os.MAC_10_15,
     properties = {
-        "xcode_build_version": "x12a8179i_audio",
+        "xcode_build_version": "12a8179i_audio",
     },
 )