crypto/internal/edwards25519: shorten quick.Check tests in short mode

crypto/internal/edwards25519: shorten quick.Check tests in short mode

The edwards25519 tests can be quite slow on platforms without a
well-optimized implementation, especially if the race detector is also
enabled. Since these tests aren't checking for specific inputs anyway,
the extra coverage of a more aggressive quick.Config does not seem
worth wasting extra time on slow CI builders and TryBots.

For #60109.

Change-Id: I530e75a0b76725585df5a2f5ded6705ab1b9da51
Reviewed-on: https://go-review.googlesource.com/c/go/+/522715
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Joedian Reid <joedian@golang.org>