runtime: fix min/max logic in findScavengeCandidate
Before this CL, if max > min and max was unaligned to min, then the
function could return an unaligned (unaligned to min) region to
scavenge. On most platforms, this leads to some kind of crash.
Fix this by explicitly aligning max to the next multiple of min.
Fixes #35445.
Updates #35112.
Change-Id: I0af42d4a307b48a97e47ed152c619d77b0298291
Reviewed-on: https://go-review.googlesource.com/c/go/+/206277 Reviewed-by: Ian Lance Taylor <iant@golang.org>