Set Codecov token

Signed-off-by: Yuki Okushi <[email protected]>

Author: JohnTitor

.github/workflows/main.yml

@@ -31,7 +31,8 @@ jobs:
         run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           files: lcov.info
           fail_ci_if_error: true
+          token: ${{ secrets.CODECOV_TOKEN }}