Update dependencies from https://github.com/dotnet/arcade build 20200909.8 (#8484)

[release/5.0.1xx-rc2] Update dependencies from dotnet/arcade
- Coherency Updates:
  - Microsoft.SourceLink.GitHub: from 1.1.0-beta-20206-02 to 1.1.0-beta-20457-02 (parent: Microsoft.DotNet.Arcade.Sdk)

eng/common/post-build/publish-using-darc.ps1

@@ -8,7 +8,7 @@ param(
   [Parameter(Mandatory=$false)][string] $EnableSourceLinkValidation,
   [Parameter(Mandatory=$false)][string] $EnableSigningValidation,
   [Parameter(Mandatory=$false)][string] $EnableNugetValidation,
-  [Parameter(Mandatory=$true)][string] $PublishInstallersAndChecksums,
+  [Parameter(Mandatory=$false)][string] $PublishInstallersAndChecksums,
   [Parameter(Mandatory=$false)][string] $ArtifactsPublishingAdditionalParameters,
   [Parameter(Mandatory=$false)][string] $SigningValidationAdditionalParameters
 )
@@ -16,7 +16,7 @@ param(
 try {
   . $PSScriptRoot\post-build-utils.ps1
   # Hard coding darc version till the next arcade-services roll out, cos this version has required API changes for darc add-build-to-channel
-  . $PSScriptRoot\..\darc-init.ps1 -darcVersion "1.1.0-beta.20418.1"
+  $darc = Get-Darc "1.1.0-beta.20418.1"
 
   $optionalParams = [System.Collections.ArrayList]::new()
 
@@ -29,7 +29,7 @@ try {
     $optionalParams.Add("--no-wait") | Out-Null
   }
 
-  if ("true" -eq $PublishInstallersAndChecksums) {
+  if ("false" -ne $PublishInstallersAndChecksums) {
     $optionalParams.Add("--publish-installers-and-checksums") | Out-Null
   }
 
@@ -50,7 +50,7 @@ try {
     }
   }
 
-  & darc add-build-to-channel `
+  & $darc add-build-to-channel `
   --id $buildId `
   --publishing-infra-version $PublishingInfraVersion `
   --default-channels `