docs: Fix dnf config-manager command

Author: markgoddard

doc/source/operations/tempest.rst

@@ -70,7 +70,7 @@ Installing Docker on Rocky:
 .. code-block:: bash
 
     sudo dnf install -y dnf-utils
-    sudo dnf-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
+    sudo dnf config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
     sudo dnf install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
 
 Ensure Docker is running & enabled: