[docs] Enhance container selection in docker dump (#14292)

* Enhance container selection in docker dump

The problem with the previous query was, that it sometimes selected multiple containers, which make the command file with a hard to understand message. Now, use '^...$' to make sure a regex full match.

docs/content/doc/usage/backup-and-restore.en-us.md

@@ -57,7 +57,7 @@ The command has to be executed with the `RUN_USER = <OS_USERNAME>` specified in
 Example:
 
 ```none
-docker exec -u <OS_USERNAME> -it -w <--tempdir> $(docker ps -qf "name=<NAME_OF_DOCKER_CONTAINER>") bash -c '/app/gitea/gitea dump -c </path/to/app.ini>'
+docker exec -u <OS_USERNAME> -it -w <--tempdir> $(docker ps -qf 'name=^<NAME_OF_DOCKER_CONTAINER>$') bash -c '/app/gitea/gitea dump -c </path/to/app.ini>'
 ```
 
 \*Note: `--tempdir` refers to the temporary directory of the docker environment used by Gitea; if you have not specified a custom `--tempdir`, then Gitea uses `/tmp` or the `TMPDIR` environment variable of the docker container. For `--tempdir` adjust your `docker exec` command options accordingly.