Remove unused IFS from test workflow

This has been present since moving from Travis CI to GitHub Actions.
IFS controls how bash splits words, but we don't do any fancy
word-splitting after that, so it's unused.

Author: senekor

.github/workflows/main.yml

@@ -18,7 +18,6 @@ jobs:
       - name: Test
         run: |
           set -euo pipefail
-          IFS=$'\n\t'
           # Check if the code is good
           cargo build --all --locked
           cargo clippy -- --deny warnings