CI: Upgrade to codecov-action@v5, and use an org-wide CODECOV_TOKEN (#247)

Author: DilumAluthge

.github/workflows/ci.yml

@@ -49,6 +49,7 @@ jobs:
           # subscriptions@julialang
           # Tell them that the +alias is +githubtestbot
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v1
+      - uses: codecov/codecov-action@v5
         with:
-          file: lcov.info
+          files: lcov.info
+          token: ${{ secrets.CODECOV_TOKEN }}