Auto merge of #14119 - eth3lbert:snapbox-uuv, r=epage

test: migrate unit_graph, update and vendor to snapbox

### What does this PR try to resolve?

Part of #14039.

Migrate following to snapbox:

- `tests/testsuite/unit_graph.rs`
- `tests/testsuite/update.rs`
- `tests/testsuite/vendor.rs`

Author: bors