Removes unnecessary dot in regexp

A string S matches ([.]|\b)html if an only if matches \bhtml:

  * If S matches [.]html, then it matches \bhtml.

  * If S matches \bhtml, then it matches \bhtml.

Reciprocally:

  * If S matches \bhtml, then it matches ([.]|\b)html.

The character class can be removed, and since we are on it we remove the
group too so that it is clear to a reader of the code that there is no
grouping going on.

References #35166.

actionview/lib/action_view/helpers/translation_helper.rb

@@ -138,7 +138,7 @@ def scope_key_by_partial(key)
         end
 
         def html_safe_translation_key?(key)
-          /([_.]|\b)html\z/.match?(key.to_s)
+          /(?:_|\b)html\z/.match?(key.to_s)
         end
     end
   end