steno_dictionary: fix handling of read-only flag

If the class implementation is marked as read-only,
then loading from a writable file should still
result in a read-only dictionary.

plover/steno_dictionary.py

@@ -62,8 +62,9 @@ def load(cls, resource):
         timestamp = resource_timestamp(filename)
         d = cls()
         d._load(filename)
-        if resource.startswith(ASSET_SCHEME) or \
-           not os.access(filename, os.W_OK):
+        if (cls.readonly or
+            resource.startswith(ASSET_SCHEME) or
+            not os.access(filename, os.W_OK)):
             d.readonly = True
         d.path = resource
         d.timestamp = timestamp

plover_build_utils/testing/steno_dictionary.py

@@ -40,6 +40,14 @@ def parse_entries(entries):
             for k, v in ast.literal_eval('{' + entries + '}').items()
         }
 
+    def test_readonly_writable_file(self, tmp_path):
+        '''
+        Writable file: match class read-only attribute.
+        '''
+        with self.sample_dict(tmp_path) as dict_path:
+            d = self.DICT_CLASS.load(str(dict_path))
+            assert d.readonly == self.DICT_CLASS.readonly
+
     def test_readonly_readonly_file(self, tmp_path):
         '''
         Read-only file: read-only dictionary.