Add missing =back

Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3117)

doc/man3/SSL_get_version.pod

@@ -86,6 +86,8 @@ The connection uses the TLSv1.2 protocol.
 
 The connection uses the TLSv1.3 protocol.
 
+=back
+
 =head1 SEE ALSO
 
 L<ssl(7)>