Update Versions.props to Preview 7 (#10937)

Author: mmitche

eng/Versions.props

@@ -5,7 +5,7 @@
     <MinorVersion>0</MinorVersion>
     <PatchVersion>0</PatchVersion>
     <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
-    <PreReleaseVersionIteration>6</PreReleaseVersionIteration>
+    <PreReleaseVersionIteration>7</PreReleaseVersionIteration>
     <VersionPrefix>$(MajorVersion).$(MinorVersion).$(PatchVersion)</VersionPrefix>
     <UseVSTestRunner>true</UseVSTestRunner>
     <!--