add workaround for cffi

.github/workflows/.tests-matrix.yaml

@@ -103,6 +103,12 @@ jobs:
         working-directory: poetry-plugin-export
         run: poetry add --lock --group dev ../poetry
 
+      # This step can be removed after having released a poetry-plugin-export version
+      # that has cffi>=1.17.0 in its lock file.
+      - name: Force more recent cffi (workaround for Python 3.13)
+        working-directory: poetry-plugin-export
+        run: poetry update --lock cffi
+
       - name: Install
         working-directory: poetry-plugin-export
         run: poetry install