CI: Fix Coverage report artifact

Fix #75
diff --git a/.gitlab/ci_nightly.yml b/.gitlab/ci_nightly.yml
index 4969deb..a71d43b 100644
--- a/.gitlab/ci_nightly.yml
+++ b/.gitlab/ci_nightly.yml
@@ -84,7 +84,9 @@
     reports:
       coverage_report:
         coverage_format: cobertura
-        path: coverage-html
+        path: coverage.xml
+    paths:
+      - coverage-html
 
 
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