MDL-85400 PHPunit: Hard to test code that uses encryption

This change stops the encryption code setting created key files to
read-only during PHPunit runs, which means they will be safely
deleted when the system resets after a test.

lib/classes/encryption.php

@@ -84,8 +84,8 @@ class encryption {
             throw new \moodle_exception('encryption_keyalreadyexists', 'error');
         }
 
-        // Don't make it read-only in Behat or it will fail to clear for future runs.
-        if (defined('BEHAT_SITE_RUNNING')) {
+        // Don't make it read-only in tests or it will fail to clear for future runs.
+        if (defined('BEHAT_SITE_RUNNING') || PHPUNIT_TEST) {
             $chmod = false;
         }