[5.x] Fixes shouldUpdateUris regex adding additional brackets to Antlers

[martyf]

This PR revises the regex to improve Antlers support in the route configuration for a Collection.

My Collection has a route of:

{{ if depth > 1 }}{{ parent_uri }}/{{ slug }}{{ else }}portal/brands/{{ slug }}{{ /if }}

The $antlersRoute with the original regex becomes:

{{ if depth > 1 }}{{{ parent_uri }}}/{{{ slug }}}{{{ else }}}portal/brands/{{{ slug }}}{{ /if }}

Notice the triple { and }?

This causes an error when saving:

Unpaired "else" control structure

This update revises the regex to allow Antlers without adding additional brackets, so the $antlersRoute correctly returns

{{ if depth > 1 }}{{ parent_uri }}/{{ slug }}{{ else }}portal/brands/{{ slug }}{{ /if }}

again.

This would also need to be rolled up to Statamic 6 too.