Fix for "uninitialized constant ViteRuby::Manifest::OpenStruct" Error

[aki77]

Description 📖

This pull request specifically targets an issue occurring only when encountering ViteRuby::MissingEntrypointError. The problem stems from the absence of require 'ostruct' in these error scenarios. This fix ensures that require 'ostruct' is included in the appropriate context, resolving the issue and preventing errors during ViteRuby::MissingEntrypointError occurrences.