refactor: migrate ENABLE_COURSE_FILENAME_CCX_SUFFIX off FEATURES-as-dict

`common/djangoapps/util/file.py` read the flag via
`settings.FEATURES.get('ENABLE_COURSE_FILENAME_CCX_SUFFIX', False)`. The
setting is defined only in lms/envs/common.py, but this reader lives in
common/ and is reachable from CMS, so use
`getattr(settings, 'ENABLE_COURSE_FILENAME_CCX_SUFFIX', False)` to avoid an
AttributeError under Studio settings. Convert the test's whole-dict
`@override_settings(FEATURES={...})` to
`@override_settings(ENABLE_COURSE_FILENAME_CCX_SUFFIX=True)`. Verified the
CCX-suffix tests pass under both lms.envs.test and cms.envs.test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: feanil

common/djangoapps/util/file.py

@@ -115,9 +115,8 @@ def course_filename_prefix_generator(course_id, separator='_'):
         course_id.run
     ])
 
-    enable_course_filename_ccx_suffix = settings.FEATURES.get(
-        'ENABLE_COURSE_FILENAME_CCX_SUFFIX',
-        False
+    enable_course_filename_ccx_suffix = getattr(
+        settings, 'ENABLE_COURSE_FILENAME_CCX_SUFFIX', False
     )
 
     if enable_course_filename_ccx_suffix and getattr(course_id, 'ccx', None):

common/djangoapps/util/tests/test_file.py

@@ -56,7 +56,7 @@ def test_locators(self, course_key):
         [CCXLocator.from_course_locator(CourseLocator(org='foo', course='bar', run='baz'), '1'), 'foo_bar_baz_ccx_1'],
     )
     @ddt.unpack
-    @override_settings(FEATURES={'ENABLE_COURSE_FILENAME_CCX_SUFFIX': True})
+    @override_settings(ENABLE_COURSE_FILENAME_CCX_SUFFIX=True)
     def test_include_ccx_id(self, course_key, expected_filename):
         """
         Test filename prefix genaration from multiple course key formats.
@@ -82,7 +82,7 @@ def test_custom_separator(self, course_key):
         [CCXLocator.from_course_locator(CourseLocator(org='foo', course='bar', run='baz'), '1'), 'foo-bar-baz-ccx-1'],
     )
     @ddt.unpack
-    @override_settings(FEATURES={'ENABLE_COURSE_FILENAME_CCX_SUFFIX': True})
+    @override_settings(ENABLE_COURSE_FILENAME_CCX_SUFFIX=True)
     def test_custom_separator_including_ccx_id(self, course_key, expected_filename):
         """
         Test filename prefix is generated with a custom separator.