api: add x509.CertPool.Equal to next/46057.txt

CL 388915 added an exported API but was authored (and tested)
before the API check became stricter.

Updates #46057.

Change-Id: Iee6e4969ade77fb0539fa97fcef0047389fb2cf6
Reviewed-on: https://go-review.googlesource.com/c/go/+/398237
Trust: Dmitri Shuralyov <[email protected]>
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>

api/next/46057.txt

@@ -0,0 +1 @@
+pkg crypto/x509, method (*CertPool) Equal(*CertPool) bool #46057