ci: drop codecov upload step (#47)

Coverage floor is already enforced by --cov-fail-under=100 in
pyproject.toml's [tool.pytest.ini_options], so codecov-action wasn't
guarding anything. Drops the step ahead of GitHub's 2026-06-16 Node 20
deprecation that would have force-upgraded codecov-action@v4.0.1 to
Node 24 with unclear effects.

Operator follow-up: the CODECOV_TOKEN repo secret is now unused and
can be deleted from Settings -> Secrets and variables -> Actions.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: lesnik512

.github/workflows/main.yml

@@ -55,11 +55,3 @@ jobs:
           PYTHONDONTWRITEBYTECODE: 1
           PYTHONUNBUFFERED: 1
           DB_DSN: postgresql+asyncpg://postgres:password@127.0.0.1/postgres
-      - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v4.0.1
-        env:
-          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
-        with:
-          files: ./coverage.xml
-          flags: unittests
-          name: codecov-${{ matrix.python-version }}