Fix failing test_checkstyle.py by changing Py3 upper limit

Now that we by default allow Python 3.6, the former whitelist being tested of allowing Python 3.6 became irrelevant. Instead, we must whitelist an interpreter that we do not allow by default, e.g. Python 3.8.

contrib/python/tests/python/pants_test/contrib/python/checks/tasks/checkstyle/test_checkstyle.py

@@ -173,7 +173,7 @@ def test_lint_runs_for_blanket_whitelist(self):
                          print(x+7)
                        """))
     target_py3 = self.make_target('a/python:fail3', PythonLibrary, sources=['fail_py3.py'],
-      compatibility=['CPython>=3.6'])
+      compatibility=['CPython>=3.8'])
     self.set_options(interpreter_constraints_whitelist=[])
     with self.assertRaises(TaskError) as task_error:
       self.execute_task(target_roots=[target_py2, target_py3])
@@ -191,7 +191,7 @@ def test_lint_runs_for_default_constraints_only(self):
                          print(x+7)
                        """))
     target_py3 = self.make_target('a/python:fail3', PythonLibrary, sources=['fail_py3.py'],
-      compatibility=['CPython>=3.6'])
+      compatibility=['CPython>=3.8'])
     with self.assertRaises(TaskError) as task_error:
       self.execute_task(target_roots=[target_py2, target_py3])
     self.assertIn('4 Python Style issues found', str(task_error.exception))
@@ -202,7 +202,7 @@ def test_lint_ignores_unwhitelisted_constraints(self):
                          print(x+7)
                        """))
     target_py3 = self.make_target('a/python:fail3', PythonLibrary, sources=['fail_py3.py'],
-      compatibility=['CPython>=3.6'])
+      compatibility=['CPython>=3.8'])
     self.assertEqual(0, self.execute_task(target_roots=[target_py3]))
 
   def test_lint_runs_for_single_whitelisted_constraints(self):
@@ -211,8 +211,8 @@ def test_lint_runs_for_single_whitelisted_constraints(self):
                          print(x+7)
                        """))
     target_py3 = self.make_target('a/python:fail3', PythonLibrary, sources=['fail_py3.py'],
-      compatibility=['CPython>=3.6'])
-    self.set_options(interpreter_constraints_whitelist=["CPython>=3.6"])
+      compatibility=['CPython>=3.8'])
+    self.set_options(interpreter_constraints_whitelist=["CPython>=3.8"])
     with self.assertRaises(TaskError) as task_error:
       self.execute_task(target_roots=[target_py3])
     self.assertIn('3 Python Style issues found', str(task_error.exception))
@@ -229,8 +229,8 @@ def test_lint_runs_for_multiple_whitelisted_constraints(self):
                          print(x+7)
                        """))
     target_py3 = self.make_target('a/python:fail3', PythonLibrary, sources=['fail_py3.py'],
-      compatibility=['CPython>=3.6'])
-    self.set_options(interpreter_constraints_whitelist=["CPython>=2.6", "CPython>=3.6"])
+      compatibility=['CPython>=3.8'])
+    self.set_options(interpreter_constraints_whitelist=["CPython>=2.6", "CPython>=3.8"])
     with self.assertRaises(TaskError) as task_error:
       self.execute_task(target_roots=[target_py2, target_py3])
     self.assertIn('7 Python Style issues found', str(task_error.exception))
@@ -247,8 +247,8 @@ def test_lint_runs_for_default_constraints_and_matching_whitelist(self):
                          print(x+7)
                        """))
     target_py3 = self.make_target('a/python:fail3', PythonLibrary, sources=['fail_py3.py'],
-      compatibility=['CPython>=3.6'])
-    self.set_options(interpreter_constraints_whitelist=["CPython>=3.6"])
+      compatibility=['CPython>=3.8'])
+    self.set_options(interpreter_constraints_whitelist=["CPython>=3.8"])
     with self.assertRaises(TaskError) as task_error:
       self.execute_task(target_roots=[target_py2, target_py3])
     self.assertIn('7 Python Style issues found', str(task_error.exception))