bug core: fix building with libstdc++

Tests: протестировано CI

---

Pull Request resolved: #1080
commit_hash:eee21ad004f184a9445d0c6fa9f8155d1fe88c84

Author: apolukhin

core/include/userver/server/http/http_request.hpp

@@ -293,7 +293,7 @@ class HttpRequest final {
     friend class HttpRequestHandler;
 
     struct Impl;
-    utils::FastPimpl<Impl, 1904, 16> pimpl_;
+    utils::FastPimpl<Impl, 1936, 16> pimpl_;
 };
 
 }  // namespace server::http