Allow passing DateTimeImmutables into format_interval.

Author: markrandall

include/branches.inc

@@ -26,8 +26,11 @@ function get_old_releases(): array
     return $cache ??= require __DIR__ . '/releases.inc';
 }
 
-function format_interval($from, DateTime $to) {
+function format_interval($from, DateTime|DateTimeImmutable $to) {
     try {
+        $from = ($from instanceof DateTimeImmutable) ? DateTime::createFromImmutable($from): $from;
+        $to = ($to instanceof DateTimeImmutable) ? DateTime::createFromImmutable($to) : $to;
+
         $from_obj = $from instanceof DateTime ? $from : new DateTime($from);
         $diff = $to->diff($from_obj);