chore: update codecov

I'm getting gpg signature errors with codecov right now. I'm going to
see if upgrading to v6 addresses the issue (unlikely, but worth a try).

Author: nfischer

.github/workflows/main.yml

@@ -18,15 +18,15 @@ jobs:
           - macos-latest
           - windows-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-node@v4
+      - uses: actions/checkout@v6
+      - uses: actions/setup-node@v6
         with:
           node-version: ${{ matrix.node-version }}
       - run: npm install
       - run: npm run test
       - run: npm run check-node-support
       - name: Upload coverage reports to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           fail_ci_if_error: true