strjoin warning in Octave

[Remi-Gau]

related to #243

Tests in CI fails on this commit in Octave only because the wrong warning gets raised in the test for append_to_layout (for example see https://github.com/bids-standard/bids-matlab/pull/243/commits/09b24289cdef02384fe6bbca00f9625745f09ddf* )

Some strjoin issue.

Could reproduce locally when running the test with moxunit but the warning does not appear outside of this context.

Giving up trying to figure it out and silencing the test for Octave only.

if anyone wants to have fun, be my guest.

[Remi-Gau]

Seems sometimes related to this:

   file_utils>canonicalise_path:189 (/github/workspace/+bids/+internal/file_utils.m)