cmd/dist: require Go 1.24.6 as minimum bootstrap toolchain
This is a minimal change to start to require the new minimum bootstrap.
Taking advantage of the newer bootstrap to simplify and improve code is
left to be done in separate CLs.
For #69315.
Change-Id: I4bef752b2adb67e969d585d97e680d26afefc6f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/694535
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>