docs: update references to renovate/renovate to v37.421.2 (#29954)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

docs/usage/docker.md

@@ -384,7 +384,7 @@ 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:37.414.1
+FROM renovate/renovate:37.421.2
 # Include the "Docker tip" which you can find here https://cloud.google.com/sdk/docs/install
 # under "Installation" for "Debian/Ubuntu"
 RUN ...