chromium_tests: apply chromium.get_env() when running tests

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.linux",
       "--builder",
       "Linux Tests",
@@ skipping 287 matching lines @@
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::isolate]/resources/find_isolated_tests.py",
       "--build-dir",
       "[SLAVE_BUILD]/src/out/Release",
       "--output-json",
       "/path/to/tmp/json"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
     "name": "find isolated tests",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"dummy_target_1\": \"[dummy hash for dummy_target_1]\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"dummy_target_2\": \"[dummy hash for dummy_target_2]\"@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@SET_BUILD_PROPERTY@swarm_hashes@{\"dummy_target_1\": \"[dummy hash for dummy_target_1]\", \"dummy_target_2\": \"[dummy hash for dummy_target_2]\"}@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/src/tools/swarming_client/run_isolated.py",
       "--isolated",
       "eeeeeeeeeeeeeeeeeeeeeeeeeeeeee",
       "-I",
       "https://isolateserver.appspot.com",
       "--verbose",
       "--",
       "--correct-common-arg",
       "--these-args-should-be-present",
       "--test-machine-name=\"Linux Tests\"",
       "--build-revision=\"f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9\"",
       "--isolated-script-test-output",
       "/path/to/tmp/json"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
     "name": "telemetry_gpu_unittests",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"failures\": [], @@@",
       "@@@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
   }
 ]