bug#46482: [core-updates] u-boot source cannot be downloaded

[Danny Milosavljevic]

failed to download 
"/gnu/store/1idpm6f9pcm9dajm90qgk6x1r6qywfv8-u-boot-2021.01.tar.bz2" from 
"ftp://ftp.denx.de/pub/u-boot/u-boot-2021.01.tar.bz2";
builder for 
`/gnu/store/5s92y4l66f8qh4p4gx79jvsjaxhl208k-u-boot-2021.01.tar.bz2.drv' failed 
to produce output path 
`/gnu/store/1idpm6f9pcm9dajm90qgk6x1r6qywfv8-u-boot-2021.01.tar.bz2'
build of /gnu/store/5s92y4l66f8qh4p4gx79jvsjaxhl208k-u-boot-2021.01.tar.bz2.drv 
failed
View build log at 
'/var/log/guix/drvs/5s/92y4l66f8qh4p4gx79jvsjaxhl208k-u-boot-2021.01.tar.bz2.drv.bz2'.
cannot build derivation 
`/gnu/store/m09apasn4glhf2lvsq8bn2ci5ncjq0fz-u-boot-tools-2021.01.drv': 1 
dependencies couldn't be built
building /gnu/store/5s4pczxlp3v8yfavmgjf93093msfaxym-ucommon-7.0.0.tar.gz.drv...

Changing the URL to "https" instead of "ftp" would work.
Changing it to "http" instead of "ftp" would also work.
Which should we use?

Reason is bug #46481.

But do we maybe want to change over to http or https anyway?

pgpuYRDVIV1yd.pgp
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