Add pypy test

.github/workflows/pypy.yml

@@ -0,0 +1,35 @@
+name:  PyPy
+on: [push, pull_request]
+
+jobs:
+  pypy:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        toolchain:
+          - {compiler: gcc, version: 12}
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up PyPy
+        uses: actions/setup-python@v5
+        with:
+          python-version: 'pypy3.9' 
+          cache: 'pip'
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install build wheel pytest
+
+      - uses: fortran-lang/setup-fortran@v1
+        id: setup-fortran
+        with:
+          compiler: ${{ matrix.toolchain.compiler }}
+          version: ${{ matrix.toolchain.version }}
+
+      - name: Build and test
+        run:
+          pypy3 -m build .
+          pypy3 -m pytest -v