PYTHON-5781 Fix TestReceiveData failures on PyPy

On PyPy, receive_data takes the wait_for_read() path before calling
recv_into(). wait_for_read() checks sock.fileno() == -1 as an early
exit; without a real return value, sock.pending() > 0 raises TypeError
on PyPy (MagicMock comparison against int is not supported).

Set fileno() = -1 on the mock so wait_for_read returns immediately.

Author: aclark4life

test/test_network_layer.py

@@ -45,6 +45,10 @@ def _make_compression_header(op_code, uncompressed_size, compressor_id):
 def _make_conn():
     conn = MagicMock()
     conn.conn.gettimeout.return_value = None
+    # PyPy calls wait_for_read() before recv_into(), which checks fileno() == -1
+    # as an early-exit. Without this, sock.fileno() returns a MagicMock and the
+    # subsequent sock.pending() > 0 comparison raises TypeError on PyPy.
+    conn.conn.sock.fileno.return_value = -1
     return conn