CI: run tests with pyproject-metadata 0.8.0rc1

Author: dnicolodi

.github/workflows/tests.yml

@@ -115,7 +115,9 @@ jobs:
         if: ${{ matrix.meson }}
 
       - name: Install
-        run: python -m pip install .[test]
+        run: |
+          python -m pip install pyproject-metadata==0.8.0rc1
+          python -m pip install .[test]
 
       - name: Run tests
         run: >-