[6.x] Update changelog for v6.18.27 with upgrade info around cookies (#36490)
[6.x] Update changelog for v6.18.27 with upgrade info around cookies (#36490)

* Update changelog for v6.18.27 with upgrade info around cookies

After this this change any existing cookies will be invalid (which may have implications for some apps)

* Update CHANGELOG-6.x.md

* Update CHANGELOG-6.x.md

Co-authored-by: Taylor Otwell <5d74ae093a16a00e5af127763f2dc7e13988f162@laravel.com>
stevebauman/framework,tomschlick/framework,hafezdivandari/framework,tomschlick/framework,laravel/framework,mul14/laravel-framework,notebowl/laravel-framework,JamesForks/framework,lucasmichot/framework,stevebauman/framework,hafezdivandari/framework,bytestream/framework,driesvints/framework,arturock/framework,crynobone/framework,bytestream/framework,mul14/laravel-framework,mul14/laravel-framework,tomschlick/framework,morrislaptop/framework,notebowl/laravel-framework,laravel/framework,lucasmichot/framework,dwightwatson/framework,JamesForks/framework,driesvints/framework,leo108/laravel_framework,arturock/framework,crynobone/framework,arturock/framework,leo108/laravel_framework,morrislaptop/framework,mul14/laravel-framework,dwightwatson/framework,samlev/framework,samlev/framework