MAINT: Update CI to use Poetry

Author: Kai-Striega

.github/workflows/pythonpackage.yml

@@ -4,14 +4,11 @@ on: [push, pull_request]
 
 jobs:
   build:
-
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
-        numpy-version: ["oldest-supported-numpy", "numpy"]
-
+        python-version: ["3.9", "3.10", "3.11"]
     steps:
     - uses: actions/checkout@v3
     - name: Set up Python ${{ matrix.python-version }}
@@ -20,19 +17,15 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip
-        pip install ${{ matrix.numpy-version }}
+        python -m pip install --upgrade pip poetry
+        poetry env use ${{ matrix.python-version }}
+        poetry install --with=test --with=lint
     - name: Lint with flake8
       run: |
-        pip install flake8
         # stop the build if there are Python syntax errors or undefined names
         flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
         flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
-    - name: Install numpy-financial
-      run: |
-        pip install .
     - name: Test with pytest
       run: |
-        pip install pytest
-        pytest
+        poetry run pytest