tests/test-check-rust-format.t

hghave: update expected rustfmt version

We still use nightly, but have moved to a newer nightly after the last
CI image upgrade in 74f1bf147a6d and 3876d4c6c79e.

#require rustfmt test-repo

  $ . "$TESTDIR/helpers-testrepo.sh"

  $ cd "$TESTDIR"/..

Warning: Keep this in sync with hghave.py
  $ RUSTFMT=$(rustup which --toolchain nightly-2024-07-16 rustfmt)
  $ for f in `testrepohg files 'glob:**/*.rs'` ; do
  >   $RUSTFMT --check --edition=2018 --unstable-features --color=never $f
  > done