nightly#49 adaptations for nightly-2025-08-31

Stream: nightly-testing

[github mathlib4 bot]

chore: adaptations for nightly-2025-08-31 nightly#49 Please review this PR. At the next toolchain release this diff will land in 'master'.

[Kim Morrison]

This one is next in line.

[Kim Morrison]

(and the diff is trivial beside the toolchain bump, so we're just looking for green CI)

[Kevin Buzzard]

Hooray we're back to PRs I can review :-)

[Bryan Gin-ge Chen]

@Kim Morrison to get bors to work here we'll need to merge #29255 first; I pinged you at #rss > mathlib bors notifications @ 💬, but it probably got buried.