config: FIX regression by prev commit "wrap all conf..."

+ Bug appeared as last 5 TCs (test_commit & test_stream) said:

  OSError: [WinError 6] The handle is invalid

Author: ankostis

git/objects/submodule/base.py

@@ -993,8 +993,8 @@ def rename(self, new_name):
                 pw.rename_section(sm_section(self.name), sm_section(new_name))
 
         # .gitmodules
-        with self.config_writer(write=True) as cw:
-            cw.config.rename_section(sm_section(self.name), sm_section(new_name))
+        with self.config_writer(write=True).config as cw:
+            cw.rename_section(sm_section(self.name), sm_section(new_name))
 
         self._name = new_name