Fix partial upgrade in the guest

A partial upgrade is often a bad idea and can cause issue like:
qemu-img: /usr/lib/libc.so.6: version `GLIBC_2.33' not found (required by qemu-img)

cow_spacesize is bumped as upgrading can use a lot of storage.

linux is ignored as we need the kernel modules for the current kernel to
be available.

Fix #136
6 jobs for partial-upgrade in 26 minutes and 16 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Lint
passed shellcheck #16184

00:00:17

passed shfmt #16185

00:00:10

 
  Build
passed build #16186
fast-single-thread

00:22:17

 
  Test
passed test-basic-qemu #16188
fast-single-thread

00:02:51

passed test-cloudimg-qemu #16189
fast-single-thread

00:03:37

passed test-vagrant-boxes-format #16187

00:00:33