test: replace explicit `padding-bottom` with `devIndicators: false` for scroll position testing (#76105)
### Why?
There were explicit `paddingBottom: 60` set to fixtures due to the dev
indicator blocking the scroll position. Since an option to disable it
was added at https://github.com/vercel/next.js/pull/76079, this PR
replaced them with `devIndicators: false`.
x-ref:
https://github.com/vercel/next.js/pull/76077#discussion_r1957164641