[pgo/mac] disable widevine signing for Mac PGO bots

enable_widevine_cdm_host_verification = false was missing from
GN args for PGO Mac bots, which is causing build failures.

Bug: 1128810
Change-Id: I2ccd1db80e80fd983e5f4ef0bd63908281557a04
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425846
Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Auto-Submit: Jeff Yoon <jeffyoon@chromium.org>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809877}

tools/mb/mb_config.pyl

@@ -2168,7 +2168,7 @@
     ],
 
     'official_goma_mac': [
-      'official', 'goma', 'no_widevine_cdm_host_verification',
+      'official', 'goma', 'no_widevine_cdm_host_verification', 'disable_widevine_signing'
     ],
 
     'official_goma_perf': [
@@ -2685,6 +2685,10 @@
       'gn_args': 'archive_seed_corpus=false',
     },
 
+    'disable_widevine_signing': {
+      'gn_args': 'enable_widevine_cdm_host_verification = false'
+    },
+
     'dx12vk': {
       # TODO(https://crbug.com/1010584): Explicitly enable DirectX 12.
       'mixins': ['enable_vulkan'],