Release `CordbUnmanagedThread` instance from `CordbProcess` member (#66910)

* Release CordbUnmanagedThread from CordbProcess member

The m_lastDispatchedIBEvent was not being cleared during shutdown, which was causing a memory leak assert to fire.
Co-authored-by: NAdeel Mujahid <3840695+am11@users.noreply.github.com>

src/coreclr/debug/di/process.cpp

@@ -1312,6 +1312,12 @@ void CordbProcess::NeuterChildren()
     m_steppers.NeuterAndClear(GetProcessLock());
 
 #ifdef FEATURE_INTEROP_DEBUGGING
+    if (m_lastDispatchedIBEvent != NULL)
+    {
+        m_lastDispatchedIBEvent->m_owner->InternalRelease();
+        m_lastDispatchedIBEvent = NULL;
+    }
+
     m_unmanagedThreads.NeuterAndClear(GetProcessLock());
 #endif // FEATURE_INTEROP_DEBUGGING