Fixes for the rename reserved paths helpers

This makes sure only the routes that belong to a certain namespace get renamed, instead of the ones that start with the same name.

Closes #32528 (closed)

And it makes sure that users get a new username when their namespace changes: #32526 (closed)

lib/gitlab/database/rename_reserved_paths_migration/v1/rename_base.rb

@@ -41,7 +41,9 @@ module Gitlab
                                             new_full_path)
             update_column_in_batches(:routes, :path, replace_statement)  do |table, query|
-              query.where(MigrationClasses::Route.arel_table[:path].matches("#{old_full_path}%"))
+              path_or_children = table[:path].eq(old_full_path)
+                                   .or(table[:path].matches("#{old_full_path}/%"))
+              query.where(path_or_children)
             end
           end