http2: fix memory leak when nghttp2 hd threshold is reached

Address: https://github.com/nodejs/node/issues/35233

nghttp2 contains a header limit as you can see here https://github.com/nghttp2/nghttp2/blob/20079b4c2f688385ba9ecf723f958d0448894879/lib/nghttp2_hd.h#L45 and when this limit is reached, the nghttp2 stops the pipelining with https://github.com/nghttp2/nghttp2/blob/master/lib/nghttp2_hd.c#L1658.

However, due to the fact of headers were processed before the error is thrown, the session still holds the memory reference for those headers and in this situation, it's never free causing the memory leak.