chore: Skip type-checking on Python 3.7

See python/mypy#14670.

duties.py

@@ -3,6 +3,7 @@
 import importlib
 import os
 import sys
+from functools import wraps
 from io import StringIO
 from pathlib import Path
 
@@ -25,6 +26,30 @@ def pyprefix(title: str) -> str:  # noqa: D103
     return title
 
 
+def skip_if(condition: bool, reason: str):
+    """Decorator allowing to skip a duty if a condition is met.
+
+    Parameters:
+        condition: The condition to meet.
+        reason: The reason to skip.
+
+    Returns:
+        A decorator.
+    """
+
+    def decorator(func):
+        @wraps(func)
+        def wrapper(ctx, *args, **kwargs):
+            if condition:
+                ctx.run(["true"], title=reason)
+            else:
+                func(ctx, *args, **kwargs)
+
+        return wrapper
+
+    return decorator
+
+
 @duty
 def changelog(ctx):
     """Update the changelog in-place with latest commits.
@@ -132,6 +157,13 @@ def check_docs(ctx):
 
 
 @duty  # noqa: WPS231
+@skip_if(
+    sys.version_info < (3, 8),
+    reason=pyprefix(
+        "Checking types is not supported on Python 3.7 because of a mypy issue, "
+        "see https://github.com/python/mypy/issues/14670"
+    ),
+)
 def check_types(ctx):  # noqa: WPS231
     """
     Check that the code is correctly typed.