crypto/tls: fix Config.Time in tests using expired certificates

crypto/tls: fix Config.Time in tests using expired certificates

Fixes #71077

Change-Id: I6a6a465685f3bd50a5bb35a160f87b59b74fa6af
Reviewed-on: https://go-review.googlesource.com/c/go/+/639655
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Ian Lance Taylor <iant@google.com>