Fixed #25968 -- Changed project/app templates to use a "py-tpl" suffix.

Debian packages unconditionally byte-compile .py files on installation and
do not silence errors by design. Therefore, we need a way of shipping these
invalid .py files without a .py extension but ensuring that when we
template them, they end up as .py.

We don't special-case .py files so that the all the TemplateCommand
command-line options (eg. extra_files and extensions) still work entirely
as expected and it may even be useful for other formats too.

tests/project_template/test_settings.py

@@ -1,13 +1,28 @@
+import os
+import shutil
 import unittest
 
+from django import conf
 from django.test import TestCase
 from django.utils import six
+from django.utils._os import upath
 
 
 @unittest.skipIf(six.PY2,
     'Python 2 cannot import the project template because '
     'django/conf/project_template doesn\'t have an __init__.py file.')
 class TestStartProjectSettings(TestCase):
+    def setUp(self):
+        # Ensure settings.py exists
+        project_dir = os.path.join(
+            os.path.dirname(upath(conf.__file__)),
+            'project_template',
+            'project_name',
+        )
+        template_settings_py = os.path.join(project_dir, 'settings.py-tpl')
+        test_settings_py = os.path.join(project_dir, 'settings.py')
+        shutil.copyfile(template_settings_py, test_settings_py)
+        self.addCleanup(os.remove, test_settings_py)
 
     def test_middleware_classes_headers(self):
         """