How to remove the possibility of walking sites on the server via https when they do not have a certificate installed?

Question

robots.txt

There is a server, I have about 10 sites on it. One of them has a domain-bound certificate installed. Installed like it should. The other 9 pieces are not protected. If you try to go to any other site on the server using the https protocol, the protocol is displayed crossed out and the site on which the certificate is installed opens. That is, if any site is assigned the https protocol, then the protected one opens. And the domain name is exactly what it should be. Those that have disallowed: / in robots.txt are also indexed by search engines because of this.

Of course, you can register redirects from https to http in htaccess, but I want to find a more competent solution.
The certificate installed through Isp manager. Server on ubuntu 16.04. Apache.