Specify windows for update galleries pipeline (#18540)

* Specify windows for update galleries pipeline

* cleanup

build/azure-pipelines/updateGalleries.yml

@@ -1,3 +1,6 @@
+pool:
+  vmImage: 'windows-latest'
+
 trigger:
 - release/extensions
 - extensions/rc1
@@ -28,8 +31,7 @@ steps:
   condition: eq(variables['Build.SourceBranch'], 'refs/heads/release/extensions')
 
 - powershell: |
-   git checkout extensions/rc1
-
+    git checkout extensions/rc1
   displayName: 'Checkout RC1 branch'
   condition: eq(variables['Build.SourceBranch'], 'refs/heads/extensions/rc1')