Add cast_alsa_cma_backend_unittests to buildbot

testing/buildbot/chromium.linux.json

 {
   "Android GN": {
     "gtest_tests": [
       {
         "test": "android_webview_unittests"
       },
       {
         "test": "base_unittests"
       },
       {
@@ skipping 408 matching lines @@
         },
         "test": "base_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "cacheinvalidation_unittests"
       },
       {
+        "test": "cast_alsa_cma_backend_unittests"
+      },
+      {
         "test": "cast_base_unittests"
       },
       {
         "test": "cast_crash_unittests"
       },
       {
         "test": "cast_media_unittests"
       },
       {
         "args": [
@@ skipping 980 matching lines @@
         "name": "mojo_apptests",
         "script": "mojo_apptests.py"
       }
     ]
   },
   "Linux Tests (dbg)(1)(32)": {
     "gtest_tests": [],
     "scripts": []
   }
 }