Update PreReleaseVersionLabel to RTM (#27885)

Author: wtgodbe

eng/Versions.props

@@ -8,7 +8,7 @@
     <MinorVersion>7</MinorVersion>
     <!-- Always use shipping version instead of dummy versions -->
     <DotNetUseShippingVersions>true</DotNetUseShippingVersions>
-    <PreReleaseVersionLabel>preview3</PreReleaseVersionLabel>
+    <PreReleaseVersionLabel>rtm</PreReleaseVersionLabel>
     <!-- Opt-in/out repo features -->
     <UsingToolIbcOptimization>true</UsingToolIbcOptimization>
     <UsingToolMicrosoftNetCompilers>true</UsingToolMicrosoftNetCompilers>