ci: add codecov token (#466)

Setting a Codecov token helps avoid throttling issues.

https://github.com/codecov/codecov-action/issues/557#issuecomment-1216749652

Signed-off-by: Michael Beemer <beeme1mr@users.noreply.github.com>

.github/workflows/merge.yml

@@ -51,6 +51,7 @@ jobs:
     - name: Upload coverage to Codecov
       uses: codecov/codecov-action@eaaf4bedf32dbdc6b720b63067d99c4d77d6047d
       with:
+        token: ${{ secrets.CODECOV_TOKEN }} # not required for public repos
         flags: unittests # optional
         name: coverage # optional
         fail_ci_if_error: true # optional (default = false)