Also parallelize the publish_snap jobs over each architecture

.azure-pipelines/templates/stages/deploy-stage.yml

@@ -37,6 +37,14 @@ stages:
           vmImage: ubuntu-18.04
         variables:
           - group: certbot-common
+        strategy:
+          matrix:
+            amd64:
+              SNAP_ARCH: amd64
+            arm32v6:
+              SNAP_ARCH: armhf
+            arm64v8:
+              SNAP_ARCH: arm64
         steps:
           - bash: |
               set -e
@@ -46,7 +54,7 @@ stages:
             displayName: Install dependencies
           - task: DownloadPipelineArtifact@2
             inputs:
-              artifact: snaps
+              artifact: snaps_$(SNAP_ARCH)
               path: $(Build.SourcesDirectory)/snap
             displayName: Retrieve Certbot snaps
           - task: DownloadSecureFile@1