Fix delta storage failing to merge node under rare circumstances (#1201)

Only fails if a node that was created after exceeding 63 readers should be merged with a node that was created before exceeding 63 readers, resulting in an `GMP===int` comparison. Affected nodes were still merged on the next `::collect()` call -> solely internal change.

src/SDK/Metrics/Stream/DeltaStorage.php

@@ -91,7 +91,7 @@ private function tryUnlink(Delta $n): void
              $c = $c->prev) {
         }
 
-        if ($c && $n->prev->readers === $c->readers) {
+        if ($c && $n->prev->readers == $c->readers) {
             $this->mergeInto($c->metric, $n->prev->metric);
             $n->prev = $n->prev->prev;
         }