Fix a URL to the NMBRTHRY list archive

Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NShane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9123)

crypto/bn/bn_sqrt.c

@@ -125,7 +125,8 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
          *         = a.
          *
          * (This is due to A.O.L. Atkin,
-         * <URL: http://listserv.nodak.edu/scripts/wa.exe?A2=ind9211&L=nmbrthry&O=T&P=562>,
+         * Subject: Square Roots and Cognate Matters modulo p=8n+5.
+         * URL: https://listserv.nodak.edu/cgi-bin/wa.exe?A2=ind9211&L=NMBRTHRY&P=4026
          * November 1992.)
          */