MK8S-25: Fix Python typing error in _get_saltenv_directories

Add proper type annotation for _get_saltenv_directories return value:
- Import Tuple from typing module
- Specify return type as Tuple[Optional[Path], Optional[Path]]
- Fixes mypy error: "Implicit generic Any. Use typing.Tuple and specify generic parameters"

Author: rdebay-scality

buildchain/buildchain/targets/repository.py

@@ -33,7 +33,7 @@
 import abc
 import operator
 from pathlib import Path
-from typing import Any, List, Optional, Sequence
+from typing import Any, List, Optional, Sequence, Tuple
 
 from buildchain import config
 from buildchain import coreutils
@@ -208,7 +208,7 @@ def clean() -> None:
             task["file_dep"].extend([self.get_rpm_path(pkg) for pkg in self.packages])
         return task
 
-    def _get_saltenv_directories(self) -> tuple:
+    def _get_saltenv_directories(self) -> Tuple[Optional[Path], Optional[Path]]:
         """Get saltenv directory paths for scality repository.
 
         Returns: