cuirass schedules aarch64 jobs on x86_64?

[Ricardo Wurmus <rekado@elephly.net>]

We have a lot of aarch64 failures that I’m manually restarting and or
building on the honeycomb machines on my desk.

Here’s one of them that fails in Cuirass:

    https://ci.guix.gnu.org/build/323991/details

And here’s the associated log:

--8<---------------cut here---------------start------------->8---
building path(s) `/gnu/store/cv9kv5x2dq1sx52rcll07isblwh9ax4a-libxtst-1.2.3'
|   @ build-started /gnu/store/pxc6wrwkwcsw2y10h48i7rkykbcjnm67-libxtst-1.2.3.drv - aarch64-linux /var/log/guix/drvs/px//c6wrwkwcsw2y10h48i7rkykbcjnm67-libxtst-1.2.3.drv.gz 49075
|   @ unsupported-platform /gnu/store/pxc6wrwkwcsw2y10h48i7rkykbcjnm67-libxtst-1.2.3.drv aarch64-linux
while setting up the build environment: a `aarch64-linux' is required to build `/gnu/store/pxc6wrwkwcsw2y10h48i7rkykbcjnm67-libxtst-1.2.3.drv', but I am a `x86_64-linux'
builder for `/gnu/store/pxc6wrwkwcsw2y10h48i7rkykbcjnm67-libxtst-1.2.3.drv' failed with exit code 1
@ build-failed /gnu/store/pxc6wrwkwcsw2y10h48i7rkykbcjnm67-libxtst-1.2.3.drv - 1 builder for `/gnu/store/pxc6wrwkwcsw2y10h48i7rkykbcjnm67-libxtst-1.2.3.drv' failed with exit code 1
--8<---------------cut here---------------end--------------->8---

What gives?

-- 
Ricardo