[c] Small update type annotation for python 3.9

headless_cms/forms.py

@@ -1,3 +1,5 @@
+from typing import Union
+
 from localized_fields.forms import LocalizedFieldForm
 from localized_fields.value import LocalizedStringValue
 from martor.fields import MartorFormField
@@ -6,7 +8,7 @@
 
 
 class _LocalizedMartorField(LocalizedFieldForm):
-    def __init__(self, *args, required: bool | list[str] = False, **kwargs):
+    def __init__(self, *args, required: Union[bool, list[str]] = False, **kwargs):
         kwargs.pop("label", None)
         super().__init__(*args, required=required, **kwargs)