Mark test_posix_proxy_sockets to depend on multithreading (#25883)

Mark test_posix_proxy_sockets to depend on multithreading to skip it in
old non-SAB capable browsers.

Author: juj

test/test_sockets.py

@@ -26,6 +26,7 @@
   requires_native_clang,
   test_file,
 )
+from test_browser import requires_shared_array_buffer
 
 from tools import config
 from tools.shared import CLANG_CC, EMCC
@@ -396,6 +397,7 @@ def test_websocket_send(self, args):
 
   # Test that native POSIX sockets API can be used by proxying calls to an intermediate WebSockets
   # -> POSIX sockets bridge server
+  @requires_shared_array_buffer
   def test_posix_proxy_sockets(self):
     # Build the websocket bridge server
     self.run_process(['cmake', path_from_root('tools/websocket_to_posix_proxy')])