ci.yml: Set --python on pipx install of Poetry.

Author: FragmentedPacket

.github/workflows/ci.yml

@@ -144,7 +144,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - name: "Setup environment"
         run: |
-          pipx install poetry==1.8.5
+          pipx install poetry==1.8.5 --python python${{ matrix.python-version }}
           poetry config virtualenvs.create true --local
           pip install invoke toml codecov
       - name: "Install Package"