Use shell=True for opening the user-provided editor with pip config

This makes the behavior compatible with git and other tools that invoke
the editor in this manner.

src/pip/_internal/commands/configuration.py

@@ -228,9 +228,13 @@ def open_in_editor(self, options: Values, args: List[str]) -> None:
         fname = self.configuration.get_file_to_edit()
         if fname is None:
             raise PipError("Could not determine appropriate file.")
+        elif '"' in fname:
+            # This shouldn't happen, unless we see a username like that.
+            # If that happens, we'd appreciate a pull request fixing this.
+            raise PipError('Can not open an editor for a file name containing ".')
 
         try:
-            subprocess.check_call([editor, fname])
+            subprocess.check_call(f'{editor} "{fname}"', shell=True)
         except FileNotFoundError as e:
             if not e.filename:
                 e.filename = editor