Exclude tkinter and turtle for Python 3.11.0 alpha7 on Ubuntu 18.04

Author: Vladimir Safonkin

tests/sources/python-modules.py

@@ -7,6 +7,7 @@
 
 import importlib
 import sys
+import platform
 
 # The Python standard library as of Python 3.0
 standard_library = [
@@ -265,6 +266,11 @@ def replace(lst, old, new):
 if sys.version_info >= (3, 11):
     standard_library.remove('binhex')
 
+# Exclude tkinter and turtle for Python 3.11 alpha temporarily
+if sys.version_info >= (3, 11) and platform.system() == 'Linux' and '18.04' in platform.version():
+    standard_library.remove('tkinter')
+    standard_library.remove('turtle')
+
 # Remove tkinter and Easter eggs
 excluded_modules = [
     'antigravity',