testutil/integration: fix nightly test behavior

[gsora]

Instead of passing errors around with channels, which in this specific test might alter timings, just panic when error is not of "context canceled" kind, during the induced restart phase.

Not ideal, but simple and effective.

category: bug ticket: none

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 58.69%. Comparing base (774902f) to head (2288df2). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3343 +/- ## ======================================= Coverage 58.68% 58.69% ======================================= Files 210 210 Lines 30290 30290 ======================================= + Hits 17777 17779 +2 + Misses 10621 10617 -4 - Partials 1892 1894 +2 ```

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