Fix typo in unittest docs (pythonGH-97742)

(cherry picked from commit e6f9ec5)

Co-authored-by: annonm <[email protected]>

Doc/library/unittest.rst

@@ -1738,7 +1738,7 @@ Loading and running tests
 
       A list of the non-fatal errors encountered while loading tests. Not reset
       by the loader at any point. Fatal errors are signalled by the relevant
-      a method raising an exception to the caller. Non-fatal errors are also
+      method raising an exception to the caller. Non-fatal errors are also
       indicated by a synthetic test that will raise the original error when
       run.