Update OSX helix queue (#59694)

Author: MackinnonBuck

eng/targets/Helix.Common.props

@@ -48,7 +48,7 @@
         <HelixAvailableTargetQueue Include="$(HelixQueueArmDebian12)" Platform="Linux" />
 
         <!-- Mac -->
-        <HelixAvailableTargetQueue Include="OSX.1200.Amd64.Open" Platform="OSX" />
+        <HelixAvailableTargetQueue Include="OSX.15.Amd64.Open" Platform="OSX" />
 
         <!-- Windows -->
         <HelixAvailableTargetQueue Include="Windows.Amd64.Server2022.Open" Platform="Windows" />