CI: Remove codecov package

This is no longer supported [1].

[1] https://about.codecov.io/blog/message-regarding-the-pypi-package/

Signed-off-by: Stephen Finucane <stephen@that.guru>

.github/workflows/ci.yaml

@@ -68,7 +68,7 @@ jobs:
         with:
           python-version: ${{ matrix.python }}
       - name: Install Python dependencies
-        run: python -m pip install tox tox-gh-actions codecov
+        run: python -m pip install tox tox-gh-actions
       - name: Log database configuration (mysql)
         if: ${{ matrix.db == 'mysql' }}
         run: |