Disallow inline config of Python version (#18497)

Fixes #18450

Author: hauntsaninja

mypy/config_parser.py

@@ -647,6 +647,11 @@ def parse_mypy_comments(
         # method is to create a config parser.
         parser = configparser.RawConfigParser()
         options, parse_errors = mypy_comments_to_config_map(line, template)
+
+        if "python_version" in options:
+            errors.append((lineno, "python_version not supported in inline configuration"))
+            del options["python_version"]
+
         parser["dummy"] = options
         errors.extend((lineno, x) for x in parse_errors)
 

test-data/unit/check-inline-config.test

@@ -323,3 +323,7 @@ class Foo:
 foo = Foo()
 if foo: ...
 42 + "no"  # type: ignore
+
+
+[case testInlinePythonVersion]
+# mypy: python-version=3.10  # E: python_version not supported in inline configuration