unit test actions on github sometimes leave dirty git tree

For example:

```
There are files left in the git tree after the tests:

?? "cmd/snap-seccomp/J\377\377\377f\017o\f\016f\017s\330\006f\017s\333\006\351<\v"

Crushing failure and despair.
```

Full log: https://pastebin.ubuntu.com/p/mKQ4gM3Ctc/