Bug#955268: udd watch: "429 too many requests" from GitHub

[Lucas Nussbaum <lucas@debian.org>]

Hi

Unfortunately, the fix in devscripts 2.20.3 doesn't work, because watch
files don't use the GitHub API, but rather URLs such as
https://github.com/osallou/cassiopee-c/tags

So different rate limiting rules apply, and authenticating using HTTP
Basic Auth doesn't work.

I ended up implementing a different workaround: when the upstream
importer hits an error 429 for github, it then skips github for the
remaining of the run.

It means that we won't add junk about software hosted on github, but
that they might get tested less frequently.

Let's see if this fixes this problem... To count packages that still
show 429 errors, use:
select count(*) from upstream where watch_file ~ 'github' and warnings ~ '429';
At this point, we are down to 3919, compared to 5200+ before I deployed
the fix.

Lucas