internal/wycheproof: update Go 1.20 crypto/ecdh API

For golang/go#56052

Change-Id: If34d01132e221ff525319e43d127ef14579f9054
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/451095
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Joedian Reid <joedian@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Joedian Reid <joedian@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

internal/wycheproof/ecdh_stdlib_test.go

@@ -118,7 +118,7 @@ func TestECDHStdLib(t *testing.T) {
 					}
 
 					shared := decodeHex(tt.Shared)
-					x, err := curve.ECDH(priv, pub)
+					x, err := priv.ECDH(pub)
 					if err != nil {
 						if tg.Curve == "curve25519" && !shouldPass {
 							// ECDH is expected to only return an error when using X25519,