[code coverage] Add xcode_build_version property to ios-simulator-code-coverage try builder.

This property is required for iOS builders running on chromium recipe.
It was removed in crrev/c/2122472 by mistake.

Change-Id: I0c4cf69ba6605ab73562d3eb125084afde828a76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2128567Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Zhaoyang Li <zhaoyangli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755417}

infra/config/buckets/try.star

@@ -577,6 +577,7 @@ try_.chromium_mac_ios_builder(
     use_clang_coverage = True,
     properties = {
         'coverage_test_types': ['unit'],
+        'xcode_build_version': '11c29',
     },
 )
 

infra/config/generated/cr-buildbucket.cfg

@@ -15595,6 +15595,7 @@ buckets: <
         properties_j: "$kitchen:{\"devshell\":true,\"git_auth\":true}"
         properties_j: "coverage_test_types:[\"unit\"]"
         properties_j: "mastername:\"tryserver.chromium.mac\""
+        properties_j: "xcode_build_version:\"11c29\""
       >
       execution_timeout_secs: 14400
       expiration_secs: 7200