test: add skip_if_running_under_valgrind()

Enable it in the USDT tests. The context (from 0xB10C):

> every time the tracepoint is reached a SIGTRAP is fired.
> No matter the tracepoint contents, even with an empty one.
> Valgrind intercepts SIGTRAP and aborts.

See discussion in #32374.

test/functional/interface_usdt_net.py

@@ -254,6 +254,7 @@ class NetTracepointTest(BitcoinTestFramework):
         self.skip_if_no_bitcoind_tracepoints()
         self.skip_if_no_python_bcc()
         self.skip_if_no_bpf_permissions()
+        self.skip_if_running_under_valgrind()
 
     def run_test(self):
         self.p2p_message_tracepoint_test()