fix: load documentation dependencies from `requirements.txt`

This CI job previously used whatever dependencies were provided by the
Jenkins node's Docker image. This change ensures the Python
dependencies are instead loaded from TF-A's PIP requirements file.

Signed-off-by: Chris Kay <chris.kay@arm.com>
Change-Id: I752125c090f3b9252be23983fe2c0eaaa326b225
1 file changed