Bump to Preview6

.github/fabricbot.json

@@ -645,7 +645,7 @@
           {
             "name": "addMilestone",
             "parameters": {
-              "milestoneName": "8.0 Preview5"
+              "milestoneName": "8.0 Preview6"
             }
           }
         ],

eng/Versions.props

@@ -4,7 +4,7 @@
     <MinorVersion>0</MinorVersion>
     <PatchVersion>0</PatchVersion>
     <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
-    <PreReleaseVersionIteration>4</PreReleaseVersionIteration>
+    <PreReleaseVersionIteration>6</PreReleaseVersionIteration>
     <VersionPrefix>$(MajorVersion).$(MinorVersion).$(PatchVersion)</VersionPrefix>
     <ValidateBaseline>true</ValidateBaseline>
     <AssemblyVersion>$(MajorVersion).$(MinorVersion).0.0</AssemblyVersion>