ci: only run publish if PKG env is set

.github/workflows/ci.yml

@@ -48,6 +48,7 @@ jobs:
                     NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
 
             -   name: Publish to S3
+                if: ${{ env.PKG != null }}
                 run: |
                     s3cmd put "${{ env.PKG }}" s3://${{ vars.S3_BUCKET }}/$(basename "${{ env.PKG }}")
 
@@ -55,7 +56,7 @@ jobs:
                     echo Release Zip SHA56: $(sha256sum "${{ env.PKG }}" | awk '{print $1}')
             -   name: Publish to Firefox
                 uses: yayuyokitano/firefox-addon@v0.0.6-alpha
-                if: ${{ github.ref_name == 'master' }}
+                if: ${{ github.ref_name == 'master' && env.PKG != null }}
                 with:
                     api_key: ${{ secrets.AMO_ISSUER }}
                     api_secret: ${{ secrets.AMO_SECRET }}