Fix samplesheet test failures: add alias column to fixtures and update assertions

[Copilot]

PR #87 added an alias column to tests/test_data/minimal-example/samplesheet.csv but left test fixtures and assertions on the old schema, causing CI to fail:

assert lines[0].replaceAll("^\uFEFF", "") == "sample,patient,timepoint,origin,file"
//                                            false
//                         actual: 'sample,alias,patient,timepoint,origin,file'

Changes

• Test fixtures — added alias column to valid_samplesheet.csv and empty_samplesheet.csv; updated minimal-example/samplesheet.csv to match PR Init channel-based reports #87's schema (alias = sample value)
• Test assertions — updated all three header assertions and the lines[1] data row check in samplesheet_check.nf.test to expect "sample,alias,patient,timepoint,origin,file"