fix wording

Co-authored-by: Bogdan Gavril <[email protected]>

Author: Ugonnaak1

msal/application.py

@@ -1848,7 +1848,7 @@ def acquire_token_by_username_password(
         is_confidential_app = self.client_credential or isinstance(
             self, ConfidentialClientApplication)
         if not is_confidential_app:
-            warnings.warn("This API has been deprecated for PCA flows, please use a more secure flow. " \
+            warnings.warn("This API has been deprecated for public client flows, please use a more secure flow. " \
             "See https://aka.ms/msal-ropc-migration for migration guidance", DeprecationWarning)
         claims = _merge_claims_challenge_and_capabilities(
                 self._client_capabilities, claims_challenge)