Explicitly fetch pristine-tar branch
We only fetch refs for tags but need pristine-tar as well for builds that need an upstream tarball. it seems older builds got this correct (likely because they were initially fetched with a broader ref pattern). Fetch pristine-tar explicitly so we're sure we get checksums right.
@arno.bauernoppel i've deliberatey not tested this since it's an exquisite case to introduce me to the test instance.
Closes: #35 (closed)