Fix GH Actions, remove Python 3.7, re-enable MacOS, remove old dev dependency (#3766)

* Fixing pytest running on incorrect Python version in GitHub actions.
Also removes 3.12 from the testing matrix, and enables MacOS again.

* Dropping Python 3.7

* Update required Python version to ^3.8

* Remove 3.7 asyncio compatibility layer

* Version pinning in GitHub Action

.github/workflows/pythonpackage.yml

@@ -16,40 +16,25 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, windows-latest]
-        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
+        os: [ubuntu-latest, windows-latest, macos-latest]
+        python-version: ["3.8", "3.9", "3.10", "3.11"]
     defaults:
       run:
         shell: bash
     steps:
-      - uses: actions/checkout@v3.5.2
-      - name: Install and configure Poetry # This could be cached, too...
-        uses: snok/install-poetry@v1.3.3
-        with:
-          version: 1.4.2
-          virtualenvs-in-project: true
+      - uses: actions/checkout@v4.1.1
+      - name: Install Poetry
+        run: pipx install poetry==1.7.1
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v4.7.1
         with:
           python-version: ${{ matrix.python-version }}
-          architecture: x64
-          allow-prereleases: true
-      - name: Load cached venv
-        id: cached-poetry-dependencies
-        uses: actions/cache@v3
-        with:
-          path: .venv
-          key: venv-${{ runner.os }}-${{ matrix.python-version }}-${{ hashFiles('**/poetry.lock') }}
+          cache: 'poetry'
       - name: Install dependencies
-        run: poetry install --extras syntax
-        if: steps.cached-poetry-dependencies.outputs.cache-hit != 'true'
-      #      - name: Typecheck with mypy
-      #        run: |
-      #          make typecheck
+        run: poetry install --no-interaction --extras syntax
       - name: Test with pytest
         run: |
-          source $VENV
-          pytest tests -v --cov=./src/textual --cov-report=xml:./coverage.xml --cov-report term-missing
+          poetry run pytest tests -v --cov=./src/textual --cov-report=xml:./coverage.xml --cov-report term-missing
       - name: Upload snapshot report
         if: always()
         uses: actions/upload-artifact@v3