osbuild: don't use bootprefix=true on aarch64 for now

Workaround an issue we are seeing where apparently the length
of the entry in the BLS config is causing systems to not boot.

- coreos/fedora-coreos-tracker#1667 (comment)
- coreos/fedora-coreos-tracker#1647 (comment)

Author: dustymabe

src/osbuild-manifests/coreos.osbuild.aarch64.mpp.yaml

@@ -111,7 +111,9 @@ pipelines:
               # because there is a symlink that is created in the root of the boot
               # filesystem by OSTree (boot -> .) that makes it so that /boot paths
               # will always work.
-              bootprefix: true
+              # XXX disabled for now because of file length BLS issue only observed on aarch64
+              # https://github.com/coreos/fedora-coreos-tracker/issues/1667#issuecomment-1967779592
+              #bootprefix: true
       - type: org.osbuild.mkdir
         options:
           paths: