Remove windows testing

Some part of `scvi-tools` is not working on windows, and since this
program will most likely be running on a linux machine or container,
we can just remove Windows support.

.github/workflows/tests.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, windows-latest]
+        os: [ubuntu-latest]
         python-version: ['3.8', '3.9', '3.10']
 
     steps: