The `test_assemblers.py` has an `assertGRUB2` helper that ensures
that the data written in the mbr and first megabyte is unchanged
by the `org.osbuild.qemu` assembler.
With the move to f38 the digests change. The mbr digest is
computed via the following python code and it matches that value
used in the test (440 byte only because the rest is the partition
table).
```
$ python3 -c 'import hashlib,sys; f=open(sys.argv[1], "rb"); m1=hashlib.sha256();m1.update(f.read()[:440]);print(m1.hexdigest())' ./f34/usr/lib/grub/i386-pc/boot.img
26e3327c6b5ac9b5e21d8b86f19ff7cb4d12fb2d0406713f936997d9d89de3ee
```
So with that code we can update the f38 mbr value now.
```
$ python3 -c 'import hashlib,sys; f=open(sys.argv[1], "rb"); m1=hashlib.sha256();m1.update(f.read()[:440]);print(m1.hexdigest())' ./f38/usr/lib/grub/i386-pc/boot.img
b8cea7475422d35cd6f85ad099fb4f921557fd1b25db62cd2a92709ace21cf0f
However computing the second sha256 for the `512:1024*1024` is much
harder to do from first principles because the value depends on the
image generated via `grub2-mkimage` and the hash changes with each
different module or config option. This means one needs to replicate
the exact inputs of:
```
subprocess.run(["grub2-mkimage",
"--verbose",
"--directory", f"/usr/lib/grub/{platform}",
"--prefix", f"(,{partid})/{grub_path}",
"--format", platform,
"--compression", "auto",
"--output", core_path] +
modules,
check=True)
```
in the test. At this point I cheated and just update to the computed
value inside the test.
2e6d49fbef