Fix separator getting added to variables_prefix when empty (#26749)

Fix separator getting added to variables_prefix

azure key vault adds a - between the key prefix and the secret name when it reads it from azure key vault. It does this even when the key prefix is "" so secrets end up named -my-secret instead of my-secret.

airflow/providers/microsoft/azure/secrets/key_vault.py

@@ -168,7 +168,11 @@ def build_path(path_prefix: str, secret_id: str, sep: str = '-') -> str:
         :param secret_id: Name of the secret
         :param sep: Separator used to concatenate path_prefix and secret_id
         """
-        path = f'{path_prefix}{sep}{secret_id}'
+        # When an empty prefix is given, do not add a separator to the secret name
+        if path_prefix == "":
+            path = f'{secret_id}'
+        else:
+            path = f'{path_prefix}{sep}{secret_id}'
         return path.replace('_', sep)
 
     def _get_secret(self, path_prefix: str, secret_id: str) -> str | None: