Polish: Improve error message clarity and comment placement

Co-authored-by: bgavrilMS <12273384+bgavrilMS@users.noreply.github.com>

Author: Copilot

msal/application.py

@@ -840,8 +840,8 @@ def _build_client(self, client_credential, authority, skip_regional_client=False
                             _extract_cert_and_thumbprints(cert))
                     else:
                         raise ValueError(
-                            "You must provide either 'thumbprint', 'thumbprint_sha256', or 'public_certificate' "
-                            "from which the thumbprint can be calculated.")
+                            "You must provide 'thumbprint' (SHA-1), 'thumbprint_sha256' (SHA-256), "
+                            "or 'public_certificate' from which the thumbprint can be calculated.")
                 else:
                     raise ValueError(
                         "client_credential needs to follow this format "

tests/test_optional_thumbprint.py

@@ -294,9 +294,7 @@ def test_pem_with_both_thumbprints_b2c_uses_sha256(
         """Test that with both thumbprints, B2C authority uses SHA-256"""
         authority = "https://contoso.b2clogin.com/contoso.onmicrosoft.com/B2C_1_susi"
         mock_authority = self._setup_mocks(mock_authority_class, authority)
-        
-        # Manually set _is_b2c to True for this B2C authority
-        mock_authority._is_b2c = True
+        mock_authority._is_b2c = True  # Manually set _is_b2c to True for this B2C authority
 
         # Create app with BOTH thumbprints for B2C
         app = ConfidentialClientApplication(