[Bug]: fix XML output for v3.9 and implement XML / ICS validation

[JohnRDOrazio]

What happened?

I hardly ever work with XML output, so I don't really test it very much. So far, the validation tools only test against JSON output. We should be able to implement XML schema validation and ICS validation in the test suite.

In any case XML output is currently broken and needs looking into.

Version

v3 (Default)

Which browser or browsers are you seeing the problem on? (can select more than one, or N/A if not applicable)

N/A

Relevant error messages

<br/>
<b>Warning</b>
:  SimpleXMLElement::addChild(): unterminated entity reference nationalcalendar=ITALY%22%2C%22year%22:%222024%22%2C%22month%22:%224%22%2C%22day%22:%2213%22%2C%22calendar%22:%22ITALY%22} in <b>/var/www/vhosts/johnromanodorazio.com/httpdocs/LiturgicalCalendar/api/dev/includes/LitFunc.php</b>
on line <b>43</b>
<br/>

[JohnRDOrazio]

fixed along with validation against an XSD schema!