Remove code coverage upload

Author: gregsvo

.github/workflows/tests.yml

@@ -46,13 +46,6 @@ jobs:
         run: |
           poetry run pytest --cov=postmark --cov-report=xml --cov-report=term
 
-      - name: Upload coverage to Codecov
-        if: matrix.python-version == '3.11'
-        uses: codecov/codecov-action@v3
-        with:
-          file: ./coverage.xml
-          fail_ci_if_error: true
-
   lint:
     runs-on: ubuntu-latest