chromium_tests: apply chromium.get_env() when running tests

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.linux",
       "--builder",
       "Linux Tests",
@@ skipping 293 matching lines @@
       "--test-launcher-summary-output",
       "/path/to/tmp/json",
       "--generate-json-file",
       "-o",
       "gtest-results/base_unittests",
       "--builder-name=Linux Tests",
       "--slave-name=TestSlavename",
       "--build-number=0",
       "base_unittests"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
     "name": "base_unittests"
   },
   {
     "allow_subannotations": true,
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/src/infra/scripts/runtest_wrapper.py",
       "--",
       "--target",
@@ skipping 11 matching lines @@
       "--generate-json-file",
       "-o",
       "gtest-results/browser_tests",
       "--builder-name=Linux Tests",
       "--slave-name=TestSlavename",
       "--build-number=0",
       "browser_tests",
       "--test-launcher-shard-index=0",
       "--test-launcher-total-shards=2"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
     "name": "browser_tests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]