samplesheetparser: add two identically-named non-colliding V1 sheets for merge collision test

[chaitanyakasaraneni]

Why two identically-named sheets

These fixtures were added to address review feedback on nf-core/modules#12774, where a reviewer asked for a samplesheetparser/merge test covering two identically-named input sheets.

The samplesheetparser/merge module takes a collection of sample sheets and merges them. In real use, per-project sheets are almost always all named SampleSheet.csv, and Nextflow raises an "input file name collision" error when two staged files share a basename. The module handles this with stageAs: "input*/*" (same pattern as samplesheetparser/diff).

To actually test that identically-named inputs are staged and merged correctly, the nf-test needs two files that share the basename SampleSheet.csv but live in separate directories (a single flat directory can't hold two files of the same name). These fixtures provide exactly that:

• bcl/samesheetparser/a/SampleSheet.csv
• bcl/samesheetparser/b/SampleSheet.csv

They are copies of the existing non-colliding V1 sheets (flowcell_samplesheet.v1.csv and flowcell_samplesheet_b.v1.csv), so the merge succeeds and the test can assert a clean result rather than a failure path. Without same-named fixtures, the collision case can only be exercised by merging a sheet with itself, which trips the index-collision check and exits non-zero.

[erikrikarddaniel]

👍 But there's a prek error.