ci: add codecov token

Author: aseyboldt

.github/workflows/coverage.yml

@@ -16,7 +16,9 @@ jobs:
       - name: Generate code coverage
         run: cargo llvm-cov --workspace --lcov --output-path lcov.info
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
         with:
           files: lcov.info
           fail_ci_if_error: true