Don't use swarming for cast_shell_browsertests on Cast Audio Linux.

testing/buildbot/chromium.linux.json

 {
   "Android Arm64 Builder (dbg)": {
     "additional_compile_targets": [
       "all"
     ]
   },
   "Android Builder": {
     "additional_compile_targets": [
       "cronet_test_instrumentation_apk",
       "system_webview_apk"
@@ skipping 2516 matching lines @@
         "test": "cast_media_unittests"
       },
       {
         "args": [
           "--enable-local-file-accesses",
           "--ozone-platform=headless",
           "--no-sandbox",
           "--test-launcher-jobs=1"
         ],
         "swarming": {
-          "can_use_on_swarming_builders": true
+          "can_use_on_swarming_builders": false
         },
         "test": "cast_shell_browsertests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "cast_shell_unittests"
       },
       {
@@ skipping 1968 matching lines @@
           "telemetry_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true,
           "shards": 4
         }
       }
     ]
   }
 }