Convert array to string

get-new-tool-versions/get-new-tool-versions.ps1

@@ -53,8 +53,9 @@ $versionsToBuild = Skip-ExistingVersions -VersionsFromManifest $versionsFromMani
                                          -VersionsFromDist $formattedVersions
 
 if ($versionsToBuild) {
-    Write-Host "The following versions are available to build:`n$versionsToBuild"
-    Write-Output "##vso[task.setvariable variable=TOOL_VERSIONS]$versionsToBuild"
+    $availableVersions = $versionsToBuild -join ","
+    Write-Host "The following versions are available to build:`n$availableVersions"
+    Write-Output "##vso[task.setvariable variable=TOOL_VERSIONS]$availableVersions"
 } else {
     Write-Host "There isn't versions to build"
 }