[ci] Explicitly list pkgconf dependency
[ci] Explicitly list pkgconf dependency

The standard Azure Pipelines images already include pkgconf so this
change has no affect. However, explicitly listing the dependencies makes
it easier to switch out to other more minimal base images.

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan