Also, fix the alert value sent when a signature by a client certificate
is invalid in TLS 1.0-1.2.

Fixes #35190

Change-Id: I2ae1d5593dfd5ee2b4d979664aec74aab4a8a704
Reviewed-on: https://go-review.googlesource.com/c/go/+/204157Reviewed-by: Katie Hockman <katie@golang.org>