Try reactivating neovim tests in CI

It has been a while since I've had to deactivate neovim in CI because of
coredumps. There were new neovim releases since then and maybe changes
in github CI.

Let's try to reactivate the tests.

.github/workflows/vader.yml

@@ -30,9 +30,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        #neovim: [false, true]
-        # When running vader tests in neovim under github's CI, it coredumps
-        neovim: [false]
+        neovim: [false, true]
 
     steps:
       - uses: actions/checkout@v2