Revise dates for legacy behaviours

A few corrections for legacy behavior dates / releases:

require_explicit_package_overrides_for_builtin_materializations is reaching "maturity" (default changing from False to True) today (release 2024.06.191), which will be rolling out gradually to dbt Cloud customers over the coming days
require_resource_names_without_spaces was introduced in 2024.05.146
The "maturity" dates in dbt Cloud for require_explicit_package_overrides_for_builtin_materializations and require_resource_names_without_spaces are still TBD. Most likely, this will be after the final release of dbt Core (OSS) v1.9 later this year.

dbt-labs / docs.getdbt.com