ci: update the test command for better output

Summary:

Now we are running the tests in neovim we get some output printed to stderr.
This is not helpful in the test output, and obfuscate errors.

This throws any unneeded output to `/dev/null` so we can focus of the tests
that have failed. It also moves over to using TAP output for a more descriptive
out put in CI.

Test Plan:

CI, running the test will validate this

.github/workflows/ci.yml

@@ -82,4 +82,4 @@ jobs:
           export VIM="${PWD}/_neovim/share/nvim/runtime"
 
           nvim --version
-          nvim -l ./scripts/busted.lua ./lua
+          nvim -l ./scripts/busted.lua -o TAP ./lua/ivy/ 2> /dev/null