Right regional endpoint for login.microsoft.com

We got it right in PR 358 based on the specs at that time, but we were using a fragile approach, which caused the "login.microsoft.com" to be left out in subsequent PR 394.

Lesson learned. Explicit is better than implicit. https://peps.python.org/pep-0020/

Author: rayluo

msal/application.py

@@ -526,8 +526,10 @@ def _get_regional_authority(self, central_authority):
         if region_to_use:
             regional_host = ("{}.r.login.microsoftonline.com".format(region_to_use)
                 if central_authority.instance in (
-                    # The list came from https://github.com/AzureAD/microsoft-authentication-library-for-python/pull/358/files#r629400328
+                    # The list came from point 3 of the algorithm section in this internal doc
+                    # https://identitydivision.visualstudio.com/DevEx/_git/AuthLibrariesApiReview?path=/PinAuthToRegion/AAD%20SDK%20Proposal%20to%20Pin%20Auth%20to%20region.md&anchor=algorithm&_a=preview
                     "login.microsoftonline.com",
+                    "login.microsoft.com",
                     "login.windows.net",
                     "sts.windows.net",
                     )