spec: Update metadata to “conditional” Stage 3

Author: js-choi

spec.html

@@ -1,7 +1,7 @@
 <pre class=metadata>
 title: ES Array.fromAsync (2022)
 status: proposal
-stage: 2
+stage: 3 (Conditional on Editor Review)
 location: https://github.com/js-choi/proposal-array-async-from
 copyright: false
 contributors: J. S. Choi