Adapt to GitHub's new env and path operations

Fixes #79

azure-pipelines/variables/_pipelines.ps1

@@ -17,7 +17,7 @@
             # and the second that works across jobs and stages but must be fully qualified when referenced.
             Write-Host "##vso[task.setvariable variable=$keyCaps;isOutput=true]$($_.Value)"
         } elseif ($env:GITHUB_ACTIONS) {
-            Write-Host "::set-env name=$keyCaps::$($_.Value)"
+            Add-Content -Path $env:GITHUB_ENV -Value "$keyCaps=$($_.Value)"
         }
         Set-Item -Path "env:$keyCaps" -Value $_.Value
     }

tools/Set-EnvVars.ps1

@@ -52,7 +52,7 @@ $Variables.GetEnumerator() |% {
         Write-Host "##vso[task.setvariable variable=$($_.Key);]$($_.Value)"
     }
     if ($env:GITHUB_ACTIONS) {
-        Write-Host "::set-env name=$($_.Key)::$($_.Value)"
+        Add-Content -Path $env:GITHUB_ENV -Value "$($_.Key)=$($_.Value)"
     }
 
     if ($cmdInstructions) {
@@ -79,7 +79,7 @@ if ($PrependPath) {
             Write-Host "##vso[task.prependpath]$_"
         }
         if ($env:GITHUB_ACTIONS) {
-            Write-Host "::add-path::$_"
+            Add-Content -Path $env:GITHUB_PATH -Value $_
         }
 
         $CmdEnvScript += "SET PATH=$_$pathDelimiter%PATH%"