covert staticmethod to instance method

Author: saadmk11

readthedocs/config/config.py

@@ -114,18 +114,17 @@ def __init__(self, key, code, error_message, source_file=None):
         self.code = code
         self.source_file = source_file
         message = self.message_template.format(
-            key=self._get_display_key(key),
+            key=self._get_display_key(),
             code=code,
             error=error_message,
         )
         super().__init__(message, code=code)
 
-    @staticmethod
-    def _get_display_key(key):
+    def _get_display_key(self):
         # Checks for patterns similar to `python.install.0.requirements`
         # if matched change to `python.install[0].requirements` using backreference.
         return re.sub(
-            r'^(python\.install)(\.)(\d+)(\.\w+)$', r'\1[\3]\4', key
+            r'^(python\.install)(\.)(\d+)(\.\w+)$', r'\1[\3]\4', self.key
         )