Build failures after updates

[martenrichter]

I get here some build failures after commit:

04700ac

I get some compiler failures with GNU 13.3.0

In file included from /home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.cc:5:
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:77:36: error: ‘constexpr’ static data member ‘string’ must have an initializer
   77 |   inline static constexpr string_t string;
      |                                    ^~~~~~
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:77:36: error: no matching function for call to ‘quiche::structured_headers::Item::string_t::string_t()’
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:74:10: note: candidate: ‘constexpr quiche::structured_headers::Item::string_t::string_t(const quiche::structured_headers::Item::string_t&)’
   74 |   struct string_t {
      |          ^~~~~~~~
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:74:10: note:   candidate expects 1 argument, 0 provided
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:74:10: note: candidate: ‘constexpr quiche::structured_headers::Item::string_t::string_t(quiche::structured_headers::Item::string_t&&)’
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:74:10: note:   candidate expects 1 argument, 0 provided
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:82:35: error: ‘constexpr’ static data member ‘token’ must have an initializer
   82 |   inline static constexpr token_t token;
      |                                   ^~~~~
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:82:35: error: no matching function for call to ‘quiche::structured_headers::Item::token_t::token_t()’
/home/runner/work/webtransport/webtransport/transports/http3-quiche/third_party/quiche/quiche/common/structured_headers.h:79:10: note: candidate: ‘constexpr quiche::structured_headers::Item::token_t::token_t(const quiche::structured_headers::Item::token_t&)’
   79 |   struct token_t {