Bug: Test multi_threaded_observable_map fails randomly

[YexuanXiao]

While fixing #1540, I noticed that the test multi_threaded_observable_map fails randomly.

> .\test multi_threaded_observable_map

Filters: multi_threaded_observable_map

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.exe is a Catch v2.13.9 host application.
Run with -? for options

-------------------------------------------------------------------------------
multi_threaded_observable_map
-------------------------------------------------------------------------------
D:\cppwinrt\test\test\multi_threaded_map.cpp(332)
...............................................................................

D:\cppwinrt\test\test\multi_threaded_map.cpp(253): FAILED:
  CHECK( moved )
with expansion:
  false

D:\cppwinrt\test\test\multi_threaded_map.cpp(253): FAILED:
  {Unknown expression after the reported line}
due to a fatal error condition:
  SIGSEGV - Segmentation violation signal

===============================================================================
test cases:   1 |   0 passed | 1 failed
assertions: 119 | 117 passed | 2 failed

cppwinrt/test/test/multi_threaded_map.cpp

Line 253 in 481f8f4

CHECK(moved);

Using the command line .\test multi_threaded_observable_map can avoid running unnecessary tests. This issue is harder to reproduce than #1540, but applying stress to the CPU to can make it easier to expose the issue (This website can apply stress to the CPU).