Fix signing step in windows CI.

Author: jgm

.github/workflows/release-candidate.yml

@@ -81,7 +81,7 @@ jobs:
         organization-id: 'd330f023-29aa-44e4-b90b-ae1c570f4a25'
         project-slug: 'pandoc'
         signing-policy-slug: 'test-signing'
-        github-artifact-id: '${{ steps.upload-unsigned-artifact.outputs.windows-release-candidate }}'
+        github-artifact-id: '${{ steps.upload-unsigned-artifact.outputs.artifact-id }}'
         wait-for-completion: true
         output-artifact-directory: 'windows-release-candidate-signed'