Rename page_header_buttons template for consistency with tag name

wagtail/admin/templatetags/wagtailadmin_tags.py

@@ -561,7 +561,7 @@ def page_listing_buttons(context, page, page_perms):
 
 
 @register.inclusion_tag(
-    "wagtailadmin/pages/listing/_modern_dropdown.html", takes_context=True
+    "wagtailadmin/pages/listing/_page_header_buttons.html", takes_context=True
 )
 def page_header_buttons(context, page, page_perms):
     next_url = context.request.path