Update pre-release label to preview (#12849)

Author: mmitche

eng/Versions.props

@@ -5,7 +5,7 @@
     <MinorVersion>0</MinorVersion>
     <PatchVersion>0</PatchVersion>
     <!-- version in our package name #.#.#-below.#####.## -->
-    <PreReleaseVersionLabel>alpha</PreReleaseVersionLabel>
+    <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
     <PreReleaseVersionIteration>1</PreReleaseVersionIteration>
     <VersionPrefix>$(MajorVersion).$(MinorVersion).$(PatchVersion)</VersionPrefix>
     <StabilizePackageVersion Condition="'$(StabilizePackageVersion)' == ''">false</StabilizePackageVersion>