Build failure because python3 isn't found

[Julien Puydt <julien.puydt@gmail.com>]

Hi,

I was surprised to see my recent upload of giac fail on most
architectures:
   https://buildd.debian.org/status/package.php?p=giac

It turned out that the common issue was:
   python3: No such file or directory

This is especially strange since :

- I use a schroot build to check for missing b-deps (but perhaps my
schroot isn't that clean?) : worked.

- I since tried to build my package in schroot on two porterbox
machines (barriere for amd64 and abel for armhf) : worked.

So I'm wondering if for some reason my package was built at a crucial
moment when something was amiss (in which case re-triggering the build
will solve the issue) or if there's really something fishy I should
investigate and solve?

Cheers,

JP