sort: use math/rand/v2 in tests and benchmarks

sort: use math/rand/v2 in tests and benchmarks

This allows to drop the use of deprecated rand.Seed in benchmarks.

Fixes #61142

Change-Id: I628848c0d4a500dc9a361930c393e47c3361a95c
Reviewed-on: https://go-review.googlesource.com/c/go/+/551155
Reviewed-by: Eli Bendersky <eliben@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
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Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
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