test: use built-in collection types for type hints (Python 3.9 / PEP 585)

Since Python 3.9, type hinting has become a little less awkward, as for
collection types one doesn't need to import the corresponding
capitalized types (`Dict`, `List`, `Set`, `Tuple`, ...) anymore, but can
use the built-in types directly. [1] [2]
This commit applies the replacement for all Python scripts (i.e. in the
contrib and test folders) for the basic types:
    - typing.Dict  -> dict
    - typing.List  -> list
    - typing.Set   -> set
    - typing.Tuple -> tuple

[1] https://docs.python.org/3.9/whatsnew/3.9.html#type-hinting-generics-in-standard-collections
[2] https://peps.python.org/pep-0585/#implementation for a list of type

test/lint/lint-files.py

@@ -11,7 +11,7 @@ import os
 import re
 import sys
 from subprocess import check_output
-from typing import Dict, Optional, NoReturn
+from typing import Optional, NoReturn
 
 CMD_TOP_LEVEL = ["git", "rev-parse", "--show-toplevel"]
 CMD_ALL_FILES = ["git", "ls-files", "-z", "--full-name", "--stage"]
@@ -69,7 +69,7 @@ class FileMeta(object):
             return None
 
 
-def get_git_file_metadata() -> Dict[str, FileMeta]:
+def get_git_file_metadata() -> dict[str, FileMeta]:
     '''
     Return a dictionary mapping the name of all files in the repository to git tree metadata.
     '''