So github got back to me and suggested to verify the email address.
Github actually works correctly. If the build fails, it sends an email
to the email account associated with the planetsympy2 user. I totally
forget to check it. So I did and it said that the build failed and I
need to verify the email address. So I did. And now it seems to be
working!
Matthew, would you mind keeping an eye on the
planet.sympy.org for a
while? I think it will be working now, but if not, please ping me.
Ondrej