MINOR: mux-quic: set both EOI EOS for stream fin

MINOR: mux-quic: set both EOI EOS for stream fin

A recent review was done to rationalize ERR/EOS/EOI flags on stream
endpoint. A common definition for both H1/H2/QUIC mux have been written
in the following documentation :
 ./doc/internals/stconn-close.txt

Always set EOS with EOI flag to conform to this specification. EOI is
set whenever the proper stream end has been encountered : with QUIC it
corresponds to a STREAM frame with FIN bit. At this step, RESET_STREAM
frames are ignored by QUIC MUX as allowed by RFC 9000. This means we can
always set EOS at the same time with EOI.

This should be backported up to 2.7.