Fix alignment of CONTEXT variable

The previous code had the `alignas()` in the wrong place, it needs to be
left of the typename.

Furthermore, `CONTEXT` has a default alignment of 16, so using `alignas(8)`
underaligns.

Signed-off-by: Chris Burel <burelc@amazon.com>

Code/Framework/AzCore/Platform/Windows/AzCore/Debug/StackTracer_Windows.cpp

@@ -1036,7 +1036,7 @@ cleanup:
             }
 
             HANDLE hThread = nativeThread;
-            CONTEXT alignas(8) context; // Without this alignment the function randomly crashes in release.
+            alignas(alignof(CONTEXT)) CONTEXT context; // Without this alignment the function randomly crashes in release.
             context.ContextFlags = CONTEXT_ALL;
             GetThreadContext(hThread, &context);