Fix #421

[RobertoPrevato]

• Fixes #421 reported by @mohd-akram, causing handled exceptions to be logged like unhandled, when defining exception handlers using subclasses.
• Removes wrong type annotations in two functions in blacksheep.utils.

[codecov-commenter]

Codecov Report

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

Comparison is base (fc9e82d) 97.46% compared to head (0bf03f5) 97.48%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #458 +/- ## ========================================== + Coverage 97.46% 97.48% +0.01% ========================================== Files 67 67 Lines 6363 6363 ========================================== + Hits 6202 6203 +1 + Misses 161 160 -1 ```

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