Add tests for `ktsctl` formula

[rosingrind]

Use homebrew docs as a reference. As ktsctl may be tested more exhaustively, implement the test case:

• place either config.toml or part of it (example) to $XDG_DATA_DIR/kak-tree-sitter (see dirs crate for details)
• execute ktsctl -f
• check if $TMPDIR/ktsctl/** really exists