Code.gs

var MAIL_SEARCH_QUERY = '[from:no_reply@email.apple.com is:unread APP_NAME "has completed processing"]';
var BITRISE_APP_SLUG = APP_SLUG;
var BITRISE_BUILD_TRIGGER_TOKEN = BUILD_TRIGGER_TOKEN;
var BRANCH_NAME = BRANCH_NAME;
var WORKFLOW_NAME = WORKFLOW_NAME;

var executeBitriseWorkflow = function() {
  var payload = {
    "payload": {
      "hook_info": {
        "type": "bitrise",
        "build_trigger_token": BITRISE_BUILD_TRIGGER_TOKEN
      },
      "build_params": {
        "branch": BRANCH_NAME,
        "workflow_id": WORKFLOW_NAME
      }
    }
  };

  var headers = {
    "Content-Type": "application/json"
  };

  var options = {
    "method": "POST",
    "headers": headers,
    "payload": JSON.stringify(payload)
  };

  var url = "https://app.bitrise.io/app/" + BITRISE_APP_SLUG + "/build/start.json";
  UrlFetchApp.fetch(url, options);
};

function main() {
  var threads = GmailApp.search(MAIL_SEARCH_QUERY);
  if (threads.length == 0) {
    return;
  }

  executeBitriseWorkflow();

  for (var i = 0; i < threads.length; i++) {
    var thread = threads[i];
    thread.markRead();  
  }
}