chore(submodule): bump etc/data/magfield from 72f3246 to a70d843 (#1428)

Bumps etc/data/magfield from `72f3246` to `a70d843`.

---
updated-dependencies:
- dependency-name: etc/data/magfield
  dependency-version: a70d84356356068928979373c1f2c8b2203a21e8
  dependency-type: direct:production
...

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