Bump laravel/framework from 6.18.19 to 6.20.26 in /laravel

Bumps [laravel/framework](https://github.com/laravel/framework) from 6.18.19 to 6.20.26.
- [Release notes](https://github.com/laravel/framework/releases)
- [Changelog](https://github.com/laravel/framework/blob/8.x/CHANGELOG-6.x.md)
- [Commits](laravel/framework@v6.18.19...v6.20.26)

Signed-off-by: dependabot[bot] <[email protected]>