`splitText` does not keep header when `keepHeader` is true and `by` is 1

Bug report

When you use splitText on a file with the keepHeader option, it does the opposite of what it's supposed to do.

Expected behavior and actual behavior

keepHeader: true removes the header, and keepHeader:false keeps the header.
The expected behaviour is that it's the other way around.

Steps to reproduce the problem

workflow {
    ch_in = Channel.fromPath('data/*tsv', checkIfExists: true)
    .map { it.splitText( keepHeader: false ).join('') }
    .view()
}

sample_A_1.tsv:

workflow {
    ch_in = Channel.fromPath('data/*tsv', checkIfExists: true)
    .map { it.splitText( keepHeader: false ).join('') }
    .view()
}

Program output

 $ nextflow run main.nf 

 N E X T F L O W   ~  version 24.10.4

Launching `main.nf` [sharp_gates] DSL2 - revision: 54c05059bf

Col1    Col2
sampleA1  tagA
sampleA1  tagB
sampleA1  tagC

Environment

• Nextflow version: 24.10.4
• Java version: openjdk 17.0.14-internal 2025-01-21
• Operating system: Linux
• Bash version: GNU bash, version 5.1.16(1)-release (x86_64-pc-linux-gnu)

Start with the splitText operator and reproduce the reported behavior using the main.nf workflow and TSV sample described in the issue, comparing keepHeader true and false when by is 1. Done means each setting preserves or removes the header according to its documented meaning, with the behavior verified against the reproduction output.