test: bump the test container size to 64 MiB

test: bump the test container size to 64 MiB

As 32 MiB appears to be on the edge of barely enough on C8S:

[  149.974689] testsuite-13.sh[601]: + dd if=/dev/zero of=/tmp/container.raw bs=1M count=32
[  150.388423] testsuite-13.sh[1096]: 32+0 records in
[  150.390721] testsuite-13.sh[1096]: 32+0 records out
[  150.392450] testsuite-13.sh[1096]: 33554432 bytes (34 MB, 32 MiB) copied, 0.354336 s, 94.7 MB/s
[  150.396422] testsuite-13.sh[601]: + mkfs.ext4 /tmp/container.raw
[  150.472209] testsuite-13.sh[1097]: mke2fs 1.45.6 (20-Mar-2020)
[  150.561303] testsuite-13.sh[1097]: Discarding device blocks: done
[  150.565438] testsuite-13.sh[1097]: Creating filesystem with 32768 1k blocks and 8192 inodes
[  150.568301] testsuite-13.sh[1097]: Filesystem UUID: d8e3c43b-0f1f-4e89-8c26-100e4a32b64f
[  150.569777] testsuite-13.sh[1097]: Superblock backups stored on blocks:
[  150.571135] testsuite-13.sh[1097]:   8193, 24577
[  150.572751] testsuite-13.sh[1097]: Allocating group tables: done
[  150.574294] testsuite-13.sh[1097]: Writing inode tables: done
[  150.598696] testsuite-13.sh[1097]: Creating journal (4096 blocks): done
[  150.604285] testsuite-13.sh[1097]: Writing superblocks and filesystem accounting information: done
[  150.612309] testsuite-13.sh[601]: + mount -o loop /tmp/container.raw /tmp/mnt
[  150.879736] testsuite-13.sh[601]: + cp -r /var/lib/machines/container1/bin ... /tmp/mnt
[  152.347545] testsuite-13.sh[1104]: cp: cannot create directory '/tmp/mnt/var/log': No space left on device
[  152.351739] testsuite-13.sh[1104]: cp: cannot create directory '/tmp/mnt/var/tmp': No space left on device