cmd/bent: always rewrite go.mod in build subdirectory

Possibility of reusing an older one could lead to inconsistent results or errors.

Change-Id: I56fdf070bb8aab25b37b0665e1878397e8992cfb
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/379539
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
1 file changed