Find partitions with the label "pmOS_inst_boot" too, and prefer using
them as boot partition over ones with label "pmOS_boot". (I'd use
"pmOS_install_boot", but there is a character limit in the label.)
Without this, the initramfs may choose the wrong boot partition if
postmarketOS is available once as install OS (on device installer) on
the SD card and once on the eMMC (installed).
I just had this problem with QEMU when simulating the install from SD to
eMMC use case with pmbootstrap qemu --second-storage. The pmOS initramfs
scripts would detect the previously created eMMC boot partition as the
proper one and mount it. It would boot into the right root partition,
because that already has a different label (pmOS_install instead of
pmOS_root), but because the wrong boot partition is already mounted,
during the install it would not be possible to run mkfs on it.
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