Don't require a tracer.root to enable a Span (#2)

Sometimes, the Span could be called inside a coroutine, then it will not have a tracer.root on its Context.

Author: leocavalcante

src/SwitchManager.php

@@ -39,10 +39,6 @@ public function apply(array $config): void
      */
     public function isEnabled(string $identifier): bool
     {
-        if (! isset($this->config[$identifier])) {
-            return false;
-        }
-
-        return $this->config[$identifier] && Context::get('tracer.root') instanceof Span;
+        return $this->config[$identifier] ?? false;
     }
 }