uhttpmock wants vapigen-0.48 but vapigen-0.50 is installed
jhbuild installs a "too new" version of vala (version 0.50 from master) but uhttpmock
locks for the specific version 0.46.
The original error is /bin/bash: [...]/jhbuild/install/bin/vapigen-0.48: [...] not found
jhbuild should pin a specific vala version to avoid this kind of issues.