[ruby/hanami] Rename DB namespace for Zeitwerk (#9279)

Fixes the following error:

    Zeitwerk::NameError: expected file /hanami/app/actions/db/index.rb
    to define constant HelloWorld::Actions::DB::Index, but didn't

Author: p8

frameworks/Ruby/hanami/app/actions/db/index.rb

@@ -2,7 +2,7 @@
 
 module HelloWorld
   module Actions
-    module Db
+    module DB
       class Index < HelloWorld::Action
         QUERY_RANGE = 1..10_000    # range of IDs in the Fortune DB
         include Deps["persistence.rom"]