[hugotest] + TEST label in hugo/introduction to check multi-version support ()

Merging branch 'hugotest'  into 'main'.

See merge request !1513

hugo/content/introduction/_index.md

 +++
-title = "Introduction"
+title = "TEST::Introduction"
 weight = 10
 +++
 
-## Introduction
+## TEST::Introduction
 
 BornAgain is an open-source research software to simulate and fit neutron and x-ray reflectometry,
 off-specular scattering, and small-angle scattering (SAS),