test: Improve test assertions to prepare for dpl query string (#90463)
*This doesn't enable skew protection for any new tests, only preparation*
Prepare a lot of test assertions so that they work correctly when a `?dpl=123` query param is present:
- some regexes should accept the query
- some places assumed that the `<script>`'s `src` is a valid pathname, whereas it might have a query param that has to be stripped before removing the path
- some hardcoded build ids instead of `next.buildId`