Add checksum of the source code tarball to the SHA256SUMS

### Description

Currently the source code tarball does **not** have a checksum listed.

```
cdba3804df7d8c00a2af674a3fe0b24c19673a0e846e5f75ac9badf227ce52f5 lima-2.2.0.tar.gz
```
It also does not get one calculcated automatically, in the interface:

```console
$ git archive --prefix lima-2.2.0/ v2.2.0 | gzip | sha256sum -
cdba3804df7d8c00a2af674a3fe0b24c19673a0e846e5f75ac9badf227ce52f5 -
```

https://github.com/lima-vm/lima/releases/tag/v2.2.0

(but nobody cares about the Source code .zip artifact)

Start with the v2.2.0 GitHub release and the shown git archive and sha256sum commands, then trace the repository's release automation that generates SHA256SUMS. Done means the source code tarball has a matching SHA256 checksum listed in SHA256SUMS for future releases.

Written by the indexing model from the issue text.