Discovered while testing MDLQA-18904

The unexpected HTML tags get generated when we intentionally changed the PUBLIC KEY and save it.

Steps to reproduce:

Setup a couple of Moodle sites:

1. Site1 running older version, for example: Moodle 4.3.x (MOODLE_403_STABLE).
2. Site2 running the version to be released (master - Moodle 4.4).
3. Ensure that they have different $CFG->sessioncookiepath setting either on config.php or in Administration > Server > Session handling
4. In both sites, enable and configure configure MNet as explained in the doc page.
5. In both sites, go to Site admin > Security > HTTP security then delete everything in "cURL blocked hosts list"
6. Please note: You don't need to configure the "remote enrolments" steps, only the "get users roaming" ones.

Testing

1. Login as admin to either site1 or site2
2. Go to Site admin > Networking > Manage peers
3. Put URL of site2 in "Hostname" then click on "Add host" and Save changes
4. Try to modify the Public key by adding or deleting some characters and Save changes
5. Verify that you were redirected to "Services" page then view source code
6. Verify that you see ul HTML tag were rendered outside the open/close html tag like the following screenshot