skip paddle.fluid.core, test=develop, test=document_fix (#23694)

tools/print_signatures.py

@@ -124,6 +124,9 @@ def visit_all_module(mod):
     if mod_name != 'paddle' and not mod_name.startswith('paddle.'):
         return
 
+    if mod_name.startswith('paddle.fluid.core'):
+        return
+
     if mod in visited_modules:
         return