fix #1203 - always export tag 280 for DICTIONARY

The export of the "hard_owned" tag (group code 280) is sometimes
necessary and sometimes not (root dictionary). Exporting this tag
even when it is not necessary seems not to break the DXF files
for AutoCAD. Therefore, this tag will always be exported to fix
issue #1203.

src/ezdxf/entities/dictionary.py

@@ -48,7 +48,7 @@
         "hard_owned": DXFAttr(
             280,
             default=1,
-            optional=True,
+            optional=False,  # 2024-11-18: changed to False because of issue #1203
             validator=validator.is_integer_bool,
             fixer=RETURN_DEFAULT,
         ),