I have solved this, and the solution is a bit easier than I thought!
outputs:
trimmed_fastq:
type:
- type: array
items: File
outputBinding:
glob: ["$(inputs.fastq_out)", "*.$(inputs.fastq_out)"]
trimmed_fastq2:
type:
- type: array
items: File
outputBinding:
glob: ["$(inputs.fastq2_out)", "*.$(inputs.fastq2_out)"]