tempfork/acme

This is a vendored copy of Tailscale's https://github.com/tailscale/golang-x-crypto, which is a fork of golang.org/x/crypto/acme.

See https://github.com/tailscale/tailscale/issues/10238 for unforking status.

The https://github.com/tailscale/golang-x-crypto location exists to let us do rebases from upstream easily, and then we update tempfork/acme in the same commit we go get github.com/tailscale/golang-x-crypto@main. See the comment on the TestSyncedToUpstream test for details. That test should catch that forgotten step.