test: add locale assertions for middleware handling#2984

pieh wants to merge 2 commits intomainopennextjs/opennextjs-netlify:mainfrom

michalpiechowiak/frb-1919-version-5113-doesnt-seem-to-pass-the-correct-locale-anymoreopennextjs/opennextjs-netlify:michalpiechowiak/frb-1919-version-5113-doesnt-seem-to-pass-the-correct-locale-anymoreCopy head branch name to clipboard