Update workflows.

This caches the virtual environment so we don't have to download it every time (the cache can be cleared from the repository > Actions > Caches (on the left).

We also split black formatting into a separate workflow.
This means we can run black ONLY when *.py files are changed.
It also means all other testing jobs don't need to _also_ check formatting.

.github/workflows/black_format.yml

@@ -0,0 +1,21 @@
+
+name: Black format check
+
+on:
+  pull_request:
+    paths:
+      - '**.py'
+
+jobs:
+  black-format-check:
+    runs-on: "ubuntu-latest"
+    steps:
+      - uses: actions/checkout@v3.5.2
+      - name: Set up Python 3.11
+        uses: actions/setup-python@v4.6.0
+        with:
+          python-version: 3.11
+      - name: Install black
+        run: python -m pip install black
+      - name: Run black
+        run: black --check src

.github/workflows/comment.yml

@@ -1,7 +1,8 @@
-name: issues
+name: Closed issue comment
 on:
   issues:
     types: [closed]
+
 jobs:
   add-comment:
     runs-on: ubuntu-latest
@@ -14,5 +15,5 @@ jobs:
           issue-number: ${{ github.event.issue.number }}
           body: |
             Don't forget to [star](https://github.com/Textualize/textual) the repository!
-            
+
             Follow [@textualizeio](https://twitter.com/textualizeio) for Textual updates.

.github/workflows/new_issue.yml

@@ -1,7 +1,8 @@
-name: issues
+name: FAQ issue comment
 on:
   issues:
     types: [opened]
+
 jobs:
   add-comment:
     if: ${{ !contains( 'willmcgugan,darrenburns,davep,rodrigogiraoserrao', github.actor ) }}

.github/workflows/pythonpackage.yml

@@ -21,27 +21,28 @@ jobs:
       run:
         shell: bash
     steps:
-      - uses: actions/checkout@v1
-      - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v2
-        with:
-          python-version: ${{ matrix.python-version }}
-          architecture: x64
-      - name: Install and configure Poetry
+      - 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
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v4.6.0
+        with:
+          python-version: ${{ matrix.python-version }}
+          architecture: x64
+      - name: Load cached venv
+        id: cached-poetry-dependencies
+        uses: actions/cache@v3
+        with:
+          path: .venv
+          key: venv-${{ runner.os }}-${{ matrix.python-version }}-${{ hashFiles('**/poetry.lock') }}
       - name: Install dependencies
         run: poetry install --extras "dev"
         if: steps.cached-poetry-dependencies.outputs.cache-hit != 'true'
-      - name: Format check with black
-        run: |
-          source $VENV
-          make format-check
 #      - name: Typecheck with mypy
 #        run: |
-#          source $VENV
 #          make typecheck
       - name: Test with pytest
         run: |