Skip testing with PyTorch 1.7 and Python 3.9 on Ubuntu (#11217)

Co-authored-by: Carlos Mocholí <carlossmocholi@gmail.com>

.github/workflows/ci_test-full.yml

@@ -28,6 +28,9 @@ jobs:
           - {os: macOS-10.15, python-version: "3.6", requires: "oldest", release: "stable"}
           # nightly: add when there's a release candidate
           #- {os: ubuntu-20.04, python-version: "3.10", requires: "latest", release: "pre"}
+        exclude:
+          # Skip if torch<1.8 and py3.9 on Linux: https://github.com/pytorch/pytorch/issues/50014
+          - {os: ubuntu-18.04, python-version: "3.9", requires: "oldest", release: "stable"}
 
     timeout-minutes: 40