Fix building for remote PR

extension/BuildPhpExtension/private/Get-ExtensionConfig.ps1

@@ -51,9 +51,13 @@ Function Get-ExtensionConfig {
                 Copy-Item $PSScriptRoot\..\config\stubs\$Extension.composer.json composer.json
             }
         }
+        $ref = $ExtensionRef
+        if ($ref -match 'refs/pull/(\d+)/merge') {
+            $ref = $Matches[1]
+        }
         $config = [PSCustomObject]@{
             name = $Extension
-            ref = $ExtensionRef
+            ref = $ref
             php_version = $PhpVersion
             arch = $Arch
             ts = $Ts

extension/BuildPhpExtension/private/Get-ExtensionSource.ps1

@@ -23,7 +23,7 @@ function Get-ExtensionSource {
             }
             if($null -eq $ExtensionRef -or $ExtensionRef -eq '') {
                 if($env:GITHUB_EVENT_NAME -contains "pull_request") {
-                    $ExtensionRef = $env:GITHUB_HEAD_REF
+                    $ExtensionRef = $env:GITHUB_REF
                 } elseif($null -ne $env:GITHUB_REF_NAME) {
                     $ExtensionRef = $env:GITHUB_REF_NAME
                 } else {