[DOCS] Fix code block length for Asciidoctor migration (#41151)

Author: jrodewig

docs/reference/setup/install/docker.asciidoc

@@ -82,7 +82,7 @@ The `vm.max_map_count` setting should be set permanently in `/etc/sysctl.conf`:
 --------------------------------------------
 $ grep vm.max_map_count /etc/sysctl.conf
 vm.max_map_count=262144
-----------------------------------
+--------------------------------------------
 
 To apply the setting on a live system type: `sysctl -w vm.max_map_count=262144`
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