Explicitly call Join() in EventLoopConnectingClientSocketTest

While google3 implementation of QUICHE thread calls join automatically, the STL-based one does not, and crashes instead if the thread has not been joined manually.

PiperOrigin-RevId: 477243248

quiche/quic/core/io/event_loop_connecting_client_socket_test.cc

diff --git a/quiche/quic/core/io/event_loop_connecting_client_socket_test.cc b/quiche/quic/core/io/event_loop_connecting_client_socket_test.cc
index a286e03..37cb607 100644
--- a/quiche/quic/core/io/event_loop_connecting_client_socket_test.cc
+++ b/quiche/quic/core/io/event_loop_connecting_client_socket_test.cc
@@ -84,7 +84,7 @@
     Start();
   }
 
-  ~TestTcpServerSocketRunner() override = default;
+  ~TestTcpServerSocketRunner() override { Join(); }
 
  protected:
   void Run() override {
@@ -124,7 +124,7 @@
     Start();
   }
 
-  ~TestUdpServerSocketRunner() override = default;
+  ~TestUdpServerSocketRunner() override { Join(); }
 
  protected:
   void Run() override {