test: bump disk sizes for some test cases

In my testing I switched building my locally run CI integration tests to
ArchLinux and realized that for that the default sizes don't work
anymore, the images are larger than the space allocated. Let's bump the
size by 50% for the relevant disk images.

test/units/TEST-13-NSPAWN.machined.sh

@@ -190,7 +190,7 @@ test ! -d /var/lib/machines/.hidden1
 
 # Prepare a simple raw container
 mkdir -p /tmp/mnt
-truncate -s 256M /var/tmp/container.raw
+truncate -s 384M /var/tmp/container.raw
 mkfs.ext4 /var/tmp/container.raw
 mount -o loop /var/tmp/container.raw /tmp/mnt
 cp -r /var/lib/machines/container1/* /tmp/mnt

test/units/TEST-13-NSPAWN.nspawn.sh

@@ -77,7 +77,7 @@ testcase_sanity() {
     create_dummy_container "$template"
     # Create a simple image from the just created container template
     image="$(mktemp /var/lib/machines/TEST-13-NSPAWN.image-XXX.img)"
-    truncate -s 256M "$image"
+    truncate -s 384M "$image"
     mkfs.ext4 "$image"
     mkdir -p /mnt
     mount -o loop "$image" /mnt