`source_url` and `source_download` do not work as expected

[francinelapid]

        source_url: <url>
        source_download: missing

does not end up downloading the source

Also, when source_download is set to latest, I get

...
Could not create builder for test stream.base (run 11797): Could not retrieve source from the given url ...
...

but a temp file with what seems like the correct content gets downloaded into the test_src directory.