ci: fix missing output on composite action (#8741)

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

.github/actions/docker-push-variables/action.yml

@@ -11,6 +11,10 @@ inputs:
     description: "Docker image arch"
 
 outputs:
+  shouldBuild:
+    description: "Whether to build image or not"
+    value: ${{ steps.ev.outputs.shouldBuild }}
+
   sha:
     description: "sha"
     value: ${{ steps.ev.outputs.sha }}