Create explicit venv in CI to fix maturin develop on Windows

Author: mstorath

.github/workflows/ci.yml

@@ -41,6 +41,16 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
+      - name: create and activate venv
+        shell: bash
+        run: |
+          python -m venv .venv
+          if [ -d .venv/Scripts ]; then
+            echo "$GITHUB_WORKSPACE/.venv/Scripts" >> "$GITHUB_PATH"
+          else
+            echo "$GITHUB_WORKSPACE/.venv/bin" >> "$GITHUB_PATH"
+          fi
+          echo "VIRTUAL_ENV=$GITHUB_WORKSPACE/.venv" >> "$GITHUB_ENV"
       - name: install build deps
         run: pip install maturin pytest numpy scipy matplotlib
       - name: maturin develop