Fix mapping for cancel cause for proto requests

[Groxx]

Pretty simple / clear missing field. No real reason to suspect other fields are similar, so I think this is all that's necessary, but it'd be really nice to have a "must fill all struct fields" linter :|

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.28%. Comparing base (ee9065f) to head (3a5b55f).
⚠️ Report is 1 commits behind head on master.
see 2 files with indirect coverage changes

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