Update appcast.xml

Author: intitni

appcast.xml

@@ -3,6 +3,18 @@
   <channel>
     <title>Copilot for Xcode</title>
 
+    <item>
+      <title>0.21.0</title>
+      <pubDate>Wed, 09 Aug 2023 15:45:24 +0800</pubDate>
+      <sparkle:version>220</sparkle:version>
+      <sparkle:shortVersionString>0.21.0</sparkle:shortVersionString>
+      <sparkle:minimumSystemVersion>12.0</sparkle:minimumSystemVersion>
+      <sparkle:releaseNotesLink>
+        https://github.com/intitni/CopilotForXcode/releases/tag/0.21.0
+      </sparkle:releaseNotesLink>
+      <enclosure url="https://github.com/intitni/CopilotForXcode/releases/download/0.21.0/Copilot.for.Xcode.app.zip" length="31114547" type="application/octet-stream" sparkle:edSignature="UFSThidzLxU/lEPfoymq2y4phSrbZRRA8JiB0NCX5Rq2n5sLkbIuRi8RK80gTk4dvSAbrvILz8GIbZYZ+GINBQ=="/>
+    </item>
+
     <item>
       <title>0.20.1</title>
       <pubDate>Fri, 21 Jul 2023 16:00:42 +0800</pubDate>