Update release label to rc (#7043)

Author: donnie-msft

build/config.props

@@ -20,7 +20,7 @@
     <!-- ** Change for each new preview/rc -->
     <!-- Check the VS schedule and manually enter a preview number here that makes sense. -->
     <!-- Preview 3 is typically the last "main branch" preview, so we start using rc at this time -->
-    <ReleaseLabel Condition=" '$(ReleaseLabel)' == '' ">preview.1</ReleaseLabel>
+    <ReleaseLabel Condition=" '$(ReleaseLabel)' == '' ">rc</ReleaseLabel>
 
     <IsEscrowMode Condition="'$(IsEscrowMode)' == ''">false</IsEscrowMode>