Install poetry just a single time

.github/workflows/main.yml

@@ -15,7 +15,20 @@ on:
 
 # A workflow run is made up of one or more jobs that can run sequentially or in parallel
 jobs:
-  # This workflow contains a single job called "build"
+  # This job is used to install Poetry
+  setup-poetry:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Poetry
+        uses: snok/install-poetry@v1
+        with:
+          version: 1.5.1
+          virtualenvs-create: true
+          virtualenvs-in-project: true
+    outputs:
+      poetry-version: ${{ steps.poetry-version.outputs.version }}
+
+  # This job is used to install dependencies and run tests for each supported Python version
   build:
     # The type of runner that the job will run on
     runs-on: ubuntu-latest
@@ -47,16 +60,12 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .venv
-          key: venv-${{ runner.os }}-${{ hashFiles('**/poetry.lock') }}
+          key: venv-${{ runner.os }}-${{ matrix.python-version }}-${{ hashFiles('**/poetry.lock') }}
 
-      - name: Select Poetry Python ${{ matrix.python-version }} Version
-        run: poetry env use ${{ matrix.python-version }}
-
-      - name: Install Python ${{ matrix.python-version }} Dependencies
+      - name: Install Dependencies
         if: steps.cached-poetry-dependencies.outputs.cache-hit != 'true'
         run: poetry install --no-interaction --no-root
 
       # Runs a single command using the runners shell
       - name: Run all tests
-        run: ./runtests
-
+        run: poetry run./runtests