Fix Dawn Mac trybot arch

Fixes mac-arm64-dawn-rel looking for x86-64 machines to run builds on
when all allocated capacity uses Apple silicon.

Bug: 1442214
Change-Id: Ibd184325d9137c06bb27b079f4a1007bd733c4d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5100850
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1234603}
diff --git a/infra/config/generated/luci/cr-buildbucket.cfg b/infra/config/generated/luci/cr-buildbucket.cfg
index 751c18c..450a05e 100644
--- a/infra/config/generated/luci/cr-buildbucket.cfg
+++ b/infra/config/generated/luci/cr-buildbucket.cfg
@@ -93567,7 +93567,6 @@
       name: "mac-arm64-dawn-rel"
       swarming_host: "chromium-swarm.appspot.com"
       dimensions: "builder:mac-arm64-dawn-rel"
-      dimensions: "cpu:x86-64"
       dimensions: "os:Mac"
       dimensions: "pool:luci.chromium.try"
       exe {
diff --git a/infra/config/subprojects/chromium/try/tryserver.chromium.dawn.star b/infra/config/subprojects/chromium/try/tryserver.chromium.dawn.star
index a529206..de8ee58 100644
--- a/infra/config/subprojects/chromium/try/tryserver.chromium.dawn.star
+++ b/infra/config/subprojects/chromium/try/tryserver.chromium.dawn.star
@@ -286,6 +286,7 @@
     ],
     gn_args = "ci/Dawn Mac arm64 Release (Apple M2)",
     os = os.MAC_ANY,
+    cpu = None,
     test_presentation = resultdb.test_presentation(
         grouping_keys = ["status", "v.test_suite", "v.gpu"],
     ),