Fix metadata file validation

[multimeric]

Cpipe checks that the input file's extensions are a subset of {fastq, gz}, when it should just check that it ends in .fastq.gz:

cpipe/lib/cpipe/metadata_schema.py

Line 32 in 642afa8

if fastq_path.exists() and set(fastq_path.suffixes).issubset({'.fastq', '.gz'}):