Fixed issue with spacing in issuable header

The Ruby was returning the HTML without a spacing next to the word 'by'

Closes #17864

app/helpers/issuables_helper.rb

@@ -72,7 +72,7 @@ module IssuablesHelper
 
   def issuable_meta(issuable, project, text)
     output = content_tag :strong, "#{text} #{issuable.to_reference}", class: "identifier"
-    output << " opened #{time_ago_with_tooltip(issuable.created_at)} by".html_safe
+    output << " opened #{time_ago_with_tooltip(issuable.created_at)} by ".html_safe
     output << content_tag(:strong) do
       author_output = link_to_member(project, issuable.author, size: 24, mobile_classes: "hidden-xs")
       author_output << link_to_member(project, issuable.author, size: 24, by_username: true, avatar: false, mobile_classes: "hidden-sm hidden-md hidden-lg")