ci: corrects coverage conditional

Author: bougyman

.github/workflows/coverage.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       # Only download this if the coverage/ directory isn't present
-      - if: !exists('coverage/index.html')
+      - if: ${{ !exists('coverage/index.html') }}
         uses: actions/download-artifact@v4
         with:
           name: coverage-report