bumps 8.18.5 to 8.18.6 (#3260)

Author: nastasha-solomon

shared/versions/stack/8.18.asciidoc

@@ -1,12 +1,12 @@
-:version:                8.18.5
+:version:                8.18.6
 ////
 bare_version never includes -alpha or -beta
 ////
-:bare_version:           8.18.5
-:logstash_version:       8.18.5
-:elasticsearch_version:  8.18.5
-:kibana_version:         8.18.5
-:apm_server_version:     8.18.5
+:bare_version:           8.18.6
+:logstash_version:       8.18.6
+:elasticsearch_version:  8.18.6
+:kibana_version:         8.18.6
+:apm_server_version:     8.18.6
 // branch is 8.18 instead of 8.x for long-term linking purposes
 :branch:                 8.18
 :minor-version:          8.18