CI: Move the buildifier check for whitespace last

[stagnation]

I always seem to trip this up, and would rather have the feedback that everything else is honky-dorey. And that the error is just a clerical omission, in the presence of well working code.

[moroten]

I thought you would prefer quick feedback before any slow compilation.

[stagnation]

Yes that too is a good point. I do not have a very strong opinion here, but want to open the discussion. As it stands I already have time for a context switch :/. I guess what I would like most is to have keep-going semantics, and return buildifier as soon as possible, but also report (in time) that everything else works.