crypto/tls: use runtime.AddCleanup instead of runtime.SetFinalizer

crypto/tls: use runtime.AddCleanup instead of runtime.SetFinalizer

Replace the usage of runtime.SetFinalizer with runtime.AddCleanup in
the certificate cache.

Updates #70907

Change-Id: Ieab6ff88dbc4083f11c1b475f11bd61521dbc638
Reviewed-on: https://go-review.googlesource.com/c/go/+/664275
Auto-Submit: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>