Minor formatting issues in NF4 RNAseq

In multisample lesson: 

- Outputs of ls operations not in collapsed admonitions
- Wrong hl_lines at [point 2.3.2](https://training.nextflow.io/latest/nf4_science/rnaseq/03_multi-sample/#232-configure-the-new-output-targets) -- leads to missing an output if copy-pasting blindly
