This commit updates the pre-existing TestJWSEncodeJSONCustom test to also verify JWS signature production works with a crypto.MessageSigner. Change-Id: I5156cb4da9a7feee98340ff4fb75848da5827055 Reviewed-on: https://go-review.googlesource.com/c/crypto/+/815480 Auto-Submit: Daniel McCarney <daniel@binaryparadox.net> Reviewed-by: Filippo Valsorda <filippo@golang.org> LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Carlos Amedee <carlos@golang.org>