Update codecov action to v3

Author: cffls

.github/workflows/main.yml

@@ -39,7 +39,7 @@ jobs:
         run: |
           poetry run pytest --doctest-modules --ignore=examples --cov=pycardano --cov-config=.coveragerc --cov-report=xml
       - name: "Upload coverage to Codecov"
-        uses: codecov/codecov-action@v2
+        uses: codecov/codecov-action@v3
         with:
           fail_ci_if_error: true