Ignore not-found errors in Sentry

[thecristen]

Summary

• Exclude DotcomWeb.NotFoundError from Sentry reporting because the router renders it as a normal 404 response.
• Add focused coverage for excluding not-found errors while keeping unexpected errors reportable.

References

• Asana: Sentry MBTA-DOTCOM-22H
• Sentry: MBTA-DOTCOM-22H

Validation

• mix test test/dotcom/sentry_test.exs — not run: dependencies are unavailable in this checkout.
• mix format --check-formatted lib/sentry.ex test/dotcom/sentry_test.exs — not run: Phoenix dependency is unavailable in this checkout.

---

• To see the specific tasks where the Asana app for GitHub is being used, see below:
  • https://app.asana.com/0/0/1219084357614128

[lvachon1]

I am unable to get the new test to run using the steps provided:

== Compilation error in file test/dotcom/sentry_test.exs ==
** (ArgumentError) the following keys must also be given when building struct Sentry.Event: [:event_id, :timestamp]
    (sentry 13.5.1) expanding struct: Sentry.Event.__struct__/1
    test/dotcom/sentry_test.exs:6: Dotcom.SentryTest."test before_send/1 ignores not found errors"/1

The other changes look fine to me.

[joshlarson]

Echoing Luc's comment, the new test causes the build to fail.

Other Sentry exclusions aren't tested, and I'm not 100% convinced that we need this one to be either.