Change search modifiers to be case-insensitive (#30865)

app/lib/search_query_transformer.rb

@@ -101,7 +101,7 @@ class SearchQueryTransformer < Parslet::Transform
   end
 
   rule(clause: subtree(:clause)) do
-    prefix   = clause[:prefix][:term].to_s if clause[:prefix]
+    prefix   = clause[:prefix][:term].to_s.downcase if clause[:prefix]
     operator = clause[:operator]&.to_s
 
     if clause[:prefix]