fix: type error on type definition

commit d0603a2 has error in type definition for mypy.
It causes ‘type’ object is not subscriptable error.

Signed-off-by: Hiroshi Miura <miurahr@linux.com>

aqt/metadata.py

@@ -393,7 +393,7 @@ def get_arch_dir_name(host: str, arch: str, version: Version) -> str:
             return arch
 
     @staticmethod
-    def default_linux_desktop_arch_dir() -> tuple[str, str]:
+    def default_linux_desktop_arch_dir() -> Tuple[str, str]:
         return ("gcc_64", "gcc_arm64")
 
     @staticmethod