Reset multisite unit tests global stack to original host after testing bootstrap

After using `_setup_host_request()` to test multiple domain and path combinations, use the same to set the global stack back to a domain of `WP_TESTS_DOMAIN` and path of `/`.

Fixes #29930


git-svn-id: https://develop.svn.wordpress.org/trunk@29881 602fd350-edb4-49c9-b593-d223f7449a82