Move away from deprecated utf_encode() on PHP 8.2+

Signed-off-by: Git'Fellow <[email protected]>

lib/private/Log/LogDetails.php

@@ -108,7 +108,7 @@ public function logDetailsAsJSON(string $app, $message, int $level): string {
 			if (is_string($value)) {
 				$testEncode = json_encode($value, JSON_UNESCAPED_SLASHES);
 				if ($testEncode === false) {
-					$entry[$key] = utf8_encode($value);
+					$entry[$key] = mb_convert_encoding($value, 'UTF-8', mb_detect_encoding($value));
 				}
 			}
 		}