Fix test_download_datasets... hopefully (#8310)

Author: NicolasHug

.github/workflows/tests-schedule.yml

@@ -29,6 +29,9 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v2
 
+      - name: TODO REMOVE THIS! Install non pre-release version of mpmath.
+        run: pip install "mpmath<1.4"
+
       - name: Install torch nightly build
         run: pip install --pre torch -f https://download.pytorch.org/whl/nightly/cpu/torch_nightly.html