chromium_tests: apply chromium.get_env() when running tests

scripts/slave/recipes/chromium.expected/dynamic_script_test_failure.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.linux",
       "--builder",
       "Linux Tests",
@@ skipping 282 matching lines @@
       "Release",
       "--use-src-side-runtest-py",
       "--paths",
       "{\"checkout\": \"[SLAVE_BUILD]/src\", \"runit.py\": \"RECIPE_PACKAGE_REPO[build]/scripts/tools/runit.py\", \"runtest.py\": \"RECIPE_PACKAGE_REPO[build]/scripts/slave/runtest.py\"}",
       "--properties",
       "{\"buildername\": \"Linux Tests\", \"buildnumber\": 571, \"mastername\": \"chromium.linux\", \"slavename\": \"TestSlavename\", \"target_platform\": \"linux\"}",
       "run",
       "--output",
       "/path/to/tmp/json"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
     "name": "test_script_with_broken_tests",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br/>failures:<br/>FailSuite.Test1<br/>FlakySuite.TestA<br/>@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"failures\": [@@@",
       "@@@STEP_LOG_LINE@json.output@    \"FailSuite.Test1\", @@@",
       "@@@STEP_LOG_LINE@json.output@    \"FlakySuite.TestA\"@@@",
       "@@@STEP_LOG_LINE@json.output@  ], @@@",
       "@@@STEP_LOG_LINE@json.output@  \"valid\": true@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]