Work around platform.python_version() returning non compliant version

src/packaging/markers.py

@@ -309,6 +309,12 @@ def evaluate(self, environment: dict[str, str] | None = None) -> bool:
         """
         current_environment = cast("dict[str, str]", default_environment())
         current_environment["extra"] = ""
+        # Work around platform.python_version() returning something that is not PEP 440
+        # compliant for non-tagged Python builds. We preserve default_environment()'s
+        # behavior of returning platform.python_version() verbatim, and leave it to the
+        # caller to provide a syntactically valid version if they want to override it.
+        if current_environment["python_full_version"].endswith("+"):
+            current_environment["python_full_version"] += "local"
         if environment is not None:
             current_environment.update(environment)
             # The API used to allow setting extra to None. We need to handle this