main/postmarketos-initramfs: umount /boot in the initramfs

Fixes a bug where the kernel thinks the boot partition is still mounted
and it's unavailable for mounting in the rootfs

#3279 (comment 454346)

main/postmarketos-initramfs/APKBUILD

 # Maintainer: Caleb Connolly <caleb@postmarketos.org>
 # Co-Maintainer: Clayton Craft <clayton@craftyguy.net>
 pkgname=postmarketos-initramfs
-pkgver=3.4.0
-pkgrel=1
+pkgver=3.4.1
+pkgrel=0
 pkgdesc="Base files for the postmarketOS initramfs / initramfs-extra"
 url="https://postmarketos.org"
 options="!check"  # no tests
@@ -105,7 +105,7 @@ sha512sums="
 9c0e8f6f61d5da191e03a1aa9d5d0ceb5baf1eae6dbb9bfb0af59817783525119ac8394b135f303f7b6434a3eab0b49185fb90379e06823db847a4999c75ce33  00-initramfs-base.dirs
 c0233d22858a5901db64e1d2fe1f6d39a2e2cfd1b94a10932483f55fed9461e9b8aa2d73b154b9d99a7a8b49ee02abfbddfe917ce0c6d7576601ba2668589c01  00-initramfs-base.files
 d0db184a5af00047b5f2c4ae869324968cdd396a17ed2c146e2523669bcf25f9ffd805eba2ec01ea74850ec674e6d0a490cdba7dcbb264bb5c512af3b212f166  00-initramfs-extra-base.files
-5dc7d65e3e6f0df07d2f7ba661dfb6714a3c3bae6a9845a6d116582780ea69e34ba5950e30fc8dd0a4852e8f2b8b1ae9ff2ea962c4c4e4b34df5e3c30d8bbb3d  init.sh
+966284e8ef8f840258a84019db4a6ddd436cdc50193e0673532f70fef86a6e4c1bfd21b682f3708251b6b670ca569c90016926d0926babc5a0257bb33ae55d79  init.sh
 bbfbec0690386e81d1a43420e7898a1e32fdf10eab88dc8d1d500a5def84c60a6dbb7055f66dc163429faf46d540dd4e8e44642b27743ea783eed6b41e0ff019  init_functions.sh
 18a0ca97bca094aeb8cb1c2582205ac0aff131085c39f1715246541cacfb35434aba515cd5d338703843efb36b9effd494a51361c51fb39be6052ad866346d3d  init_2nd.sh
 30fb52456376020e70116169752582d25a011a858111a347c2e53eccaddea8765fab502371cfdc0c2a8ca93034795b7e689e4cd3393ad601268c02024c4e84ab  init_functions_2nd.sh

main/postmarketos-initramfs/init.sh

@@ -59,6 +59,8 @@ mount_subpartitions
 wait_boot_partition
 mount_boot_partition /boot
 extract_initramfs_extra /boot/initramfs-extra
+# /boot is mounted later into the rootfs
+umount /boot
 
 # Kill mdev, since it's replaced by udev in the
 # second stage init