Install package

This should ensure that the build environment is as specified in `pyproject.toml`

.github/workflows/lint_python.yml

@@ -9,6 +9,7 @@ jobs:
             - uses: actions/checkout@v2
             - uses: actions/setup-python@v2
             - run: pip install --upgrade pip wheel
+            - run: pip install .
             - run: pip install bandit black flake8 flake8-bugbear flake8-comprehensions isort safety mypy
             - run: mypy --install-types --non-interactive --ignore-missing-imports ./rembg
             - run: bandit --recursive --skip B101,B104,B310,B311,B303 --exclude ./rembg/_version.py ./rembg