Method setHeadersGuard

github-actions/saucelabs/set-saucelabs-env.js:12583–12585

(o, guard)

          }
          if (__privateGet(this, _guard) === "immutable") {
            throw new TypeError("immutable");
          }
          __privateGet(this, _headersList).set(name, value, false);
        }
        // https://fetch.spec.whatwg.org/#dom-headers-getsetcookie
        getSetCookie() {