chore: try codecov token again

I tried this recently in 1a1a820 and
then reverted in b8b1c42. Unfortunately
I'm still seeing spurious failures from codecov, so let's try the token
one more time.

This time I double checked the token is provided by
https://app.codecov.io/gh/shelljs/shelljs/settings. I regenerated the
token for good measure.

.github/workflows/main.yml

@@ -51,4 +51,5 @@ jobs:
         if: matrix.node-version >= 10
         uses: codecov/codecov-action@v3
         with:
+          token: ${{ secrets.CODECOV_TOKEN }}
           fail_ci_if_error: true