footer-refs-validity false positive

[knocte]

+ npx commitlint --from HEAD~1 --to HEAD --verbose
⧗   input: scripts/checkCommits1by1: fix IndexOutOfRangeEx

We tried to make this script support for legit absence
of CI status via [1] but that caused IndexOutOfRangeExs.
This change now makes sure that the commitMsg is extracted
from the 1st API call (which is not dependent on a CI
status being present) so it should fix the problem (the
use of `[0]` hardcoded indexing was a big smell here that
turned out to cause this problem).

[1] 8c00fed7d2[45](https://github.com/knocte/conventions/actions/runs/7692618873/job/20959909590#step:7:46)89d7b70957cc872b1a1e57a76f93
✖   All references in the body must be mentioned in the footer, and vice versa.
For reference, these are the guidelines that include our commit message conventions: https://github.com/nblockchain/conventions/blob/master/docs/WorkflowGuidelines.md [footer-refs-validity]