Bump dropshot from 6a3f84c to fb254ad (#742)

Bumps [dropshot](https://github.com/oxidecomputer/dropshot) from `6a3f84c` to `fb254ad`.
- [Commits](oxidecomputer/dropshot@6a3f84c...fb254ad)

---
updated-dependencies:
- dependency-name: dropshot
  dependency-type: direct:production
...

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Author: dependabot[bot]