docs: update references to renovate/renovate to v29.29.0 (#12911)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

docs/usage/docker.md

@@ -229,7 +229,7 @@ To get access to the token a custom Renovate Docker image is needed that include
 The Dockerfile to create such an image can look like this:
 
 ```Dockerfile
-FROM renovate/renovate:29.14.1
+FROM renovate/renovate:29.29.0
 # Include the "Docker tip" which you can find here https://cloud.google.com/sdk/docs/install
 # under "Installation" for "Debian/Ubuntu"
 RUN ...