docs: Remove references to language_overrides (#12169)

This PR replaces references to `language_overrides` in the docs with
just `languages`.

`language_overrides` is an alias for `languages`, and we want to move
towards just using `languages`.

Release Notes:

- N/A

docs/src/languages/python.md

@@ -54,7 +54,7 @@ A common tool for formatting python code is [Black](https://black.readthedocs.io
 
 ```json
 {
-  "language_overrides": {
+  "languages": {
     "Python": {
       "format_on_save": {
         "external": {