Fix EH stacktrace keepalive array copy size (#104912)

When the stacktrace keepalive array is grown, we were incorrectly
copying extra item from the original keepalive array to the new one. In
some cases, it ended up adding garbage to the array and GC object
verification has hickuped on it. In the CI, it was only hit by
GCStress-Extra tests that set DOTNET_HeapVerify=1 so far.

This fixes the copied size to be the source array's number of elements.

Close #104878

src/coreclr/vm/excep.cpp

@@ -2975,7 +2975,7 @@ void StackTraceInfo::EnsureKeepAliveArray(PTRARRAYREF *ppKeepAliveArray, size_t
         {
             memmoveGCRefs(pNewKeepAliveArray->GetDataPtr(),
                           (*ppKeepAliveArray)->GetDataPtr(),
-                          neededSize * sizeof(Object *));        
+                          (*ppKeepAliveArray)->GetNumComponents() * sizeof(Object *));
         }
         // Update the keepAlive array
         *ppKeepAliveArray = pNewKeepAliveArray;