Avoid logging CancelledError in taskDone

[codecov[bot]]

Codecov Report

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

Project coverage is 96.27%. Comparing base (ddee10c) to head (b8be630). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3860 +/- ## ========================================== - Coverage 96.35% 96.27% -0.08% ========================================== Files 243 243 Lines 54057 54059 +2 ========================================== - Hits 52086 52046 -40 - Misses 1971 2013 +42 ``` | [Flag](https://app.codecov.io/gh/vertexproject/synapse/pull/3860/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | Coverage Δ | | |---|---|---| | [linux](https://app.codecov.io/gh/vertexproject/synapse/pull/3860/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | `96.27% <100.00%> (+<0.01%)` | :arrow_up: | | [linux_replay](https://app.codecov.io/gh/vertexproject/synapse/pull/3860/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject#carryforward-flags-in-the-pull-request-comment) to find out more.

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