Build is broken with latest version of `http2`

[mpscholten]

The HeaderList data structure has been removed and this causes the build to fail:

src/Network/HTTP2/Client/Dispatch.hs:69:40: error: [GHC-76037]
    Not in scope: type constructor or class HeaderList
   |
69 |     = StreamHeadersEvent !FrameHeader !HeaderList
   |                                        ^^^^^^^^^^

src/Network/HTTP2/Client/Dispatch.hs:70:54: error: [GHC-76037]
    Not in scope: type constructor or class HeaderList
   |
70 |     | StreamPushPromiseEvent !FrameHeader !StreamId !HeaderList
   |                                                      ^^^^^^^^^^

src/Network/HTTP2/Client/Dispatch.hs:252:25: error: [GHC-76037]
    Not in scope: type constructor or class HeaderList
    |
252 |     { _encodeHeaders :: HeaderList -> IO HeaderBlockFragment
    |                         ^^^^^^^^^^