Fix agent test setup

Instantiate a wolfSSH_AGENT_CTX before invoking wolfSSH_AGENT_SignRequest so the regression tests exercise the intended paths instead of failing with WS_AGENT_NULL_E.

Author: LinuxJedi

tests/api.c

@@ -964,6 +964,7 @@ static void setup_agent_test(WOLFSSH_CTX** ctx, WOLFSSH** ssh, AgentTestCtx* io)
     AssertIntEQ(wolfSSH_CTX_set_agent_cb(*ctx, test_agent_cb,
         test_agent_io_cb), WS_SUCCESS);
     AssertNotNull(*ssh = wolfSSH_new(*ctx));
+    AssertNotNull((*ssh)->agent = wolfSSH_AGENT_new((*ctx)->heap));
     AssertIntEQ(wolfSSH_set_agent_cb_ctx(*ssh, io), WS_SUCCESS);
     AssertIntEQ(wolfSSH_AGENT_enable(*ssh, 1), WS_SUCCESS);
 }