check_cellrangermulti.py doesn't handle BOM

### Description of the bug The `parse_samplesheet` function breaks if the CSV has a BOM. Changing the encoding of `open` to "utf-8-sig" would handle cases with or without BOM. I think the BOM can be introduced if exporting via excel on windows. ### Command used and terminal output ```console python ./bin/check_cellrangermulti.py ./assets/cellranger_barcodes_samplesheet_with_bom.csv ``` ### Relevant files You can use the attached samplesheet within the and run the cellranger_multi human test (or just run the check_cellrangermulti.py script) to replicate the failure [cellranger_barcodes_samplesheet_with_bom.csv](https://github.com/user-attachments/files/23891153/cellranger_barcodes_samplesheet_with_bom.csv) ### System information Error appearing on MacOS as well as via AWS batch in nf-core/scrnaseq v4.1.0