Add six for @to_static and add CI approval (#47575)

* Add six for @to_static and add CI approval

* add six

* refine logic

* delete approve

* fix return

* add ImportError

* typo `moduels` -> `modules`
Co-authored-by: NNyakku Shigure <sigure.qaq@gmail.com>

python/paddle/fluid/dygraph/dygraph_to_static/convert_call_func.py

@@ -50,16 +50,7 @@ from paddle.fluid.dygraph.layers import Layer
 
 __all__ = ["convert_call"]
 
-# TODO(liym27): A better way to do this.
-BUILTIN_LIKELY_MODULES = [
-    collections,
-    pdb,
-    copy,
-    inspect,
-    re,
-    numpy,
-    logging,
-]
+
 # The api(s) should be considered as plain function and convert
 # them into static layer code.
 PADDLE_NEED_CONVERT_APIS = [Sequential]
@@ -99,6 +90,32 @@ def is_builtin(func, name=None):
         return False
 
 
+def builtin_modules():
+    """
+    Return builtin modules.
+    """
+    modules = [
+        collections,
+        pdb,
+        copy,
+        inspect,
+        re,
+        numpy,
+        logging,
+    ]
+    try:
+        import six
+
+        modules.append(six)
+    except ImportError:
+        pass  # do nothing
+
+    return modules
+
+
+BUILTIN_LIKELY_MODULES = builtin_modules()
+
+
 def is_unsupported(func):
     """
     Checks whether the func is supported by dygraph to static graph.