bpo-32923: Unittest doc: replace `whilst` with `while` (GH-5833)

`whilst` and `while` are both english words, `whilst` is not as commonly used.
This can be confusing to readers whose primary language is not english.

Doc/library/unittest.rst

@@ -2316,7 +2316,7 @@ handling functionality within test frameworks.
 
    When called without arguments this function removes the control-c handler
    if it has been installed. This function can also be used as a test decorator
-   to temporarily remove the handler whilst the test is being executed::
+   to temporarily remove the handler while the test is being executed::
 
       @unittest.removeHandler
       def test_signal_handling(self):