ensure that packages that come back from AdditionalValidationPackages…

… are NOT counted as 'includedForValidation: true' if they also exist in the original 'these packages changed' set

eng/common/scripts/Package-Properties.ps1

@@ -187,12 +187,17 @@ function Get-PrPkgProperties([string]$InputDiffJson) {
         }
     }
 
+    $existingPackageNames = $packagesWithChanges | ForEach-Object { $_.Name }
     foreach ($addition in $additionalValidationPackages) {
         $key = $addition.Replace($RepoRoot, "").TrimStart('\/')
 
         if ($lookup[$key]) {
-            $lookup[$key].IncludedForValidation = $true
-            $packagesWithChanges += $lookup[$key]
+            $pkg = $lookup[$key]
+
+            if ($pkg.Name -notin $existingPackageNames) {
+                $pkg.IncludedForValidation = $true
+                $packagesWithChanges += $pkg
+            }
         }
     }