Change relative path discovery behaviour

[nebfield]

https://github.com/PGScatalog/pgsc_calc/issues/151

• We added path discovery to auto-detect compressed variant information files in the latest release
• However, the relative paths in the pgsc_calc test samplesheet aren't being resolved correctly
  • This problem only happens when running the workflow directly from nextflow (nextflow run pgscatalog/pgsc_calc)
  • Running the workflow from a cloned repository works OK
• Current behaviour is to try and resolve the relative paths starting in a nextflow work directory
• Would better behaviour be to resolve the relative paths starting in the samplesheet directory?

We would like the test profile to work in an offline environment. Most nf-core pipelines fetch test data remotely.