Declare nfds parameter of PollSyscall() as size_t

Match the type of the nfds parameter in the base class, which was
changed to size_t in cl/527603143.

PiperOrigin-RevId: 706750459

quiche/quic/core/io/quic_poll_event_loop_test.cc

diff --git a/quiche/quic/core/io/quic_poll_event_loop_test.cc b/quiche/quic/core/io/quic_poll_event_loop_test.cc
index 502757d..a0a452b 100644
--- a/quiche/quic/core/io/quic_poll_event_loop_test.cc
+++ b/quiche/quic/core/io/quic_poll_event_loop_test.cc
@@ -64,7 +64,7 @@
   QuicPollEventLoopForTest(MockClock* clock)
       : QuicPollEventLoop(clock), clock_(clock) {}
 
-  int PollSyscall(pollfd* fds, nfds_t nfds, int timeout) override {
+  int PollSyscall(pollfd* fds, size_t nfds, int timeout) override {
     timeouts_.push_back(timeout);
     if (eintr_after_ != QuicTime::Delta::Infinite()) {
       errno = EINTR;