`retry` can produce excessively large logs

[hendrikmakait]

As discussed in #8511, retry can produce very large logs if the retried coro has a very large string representation.

We can probably truncate the string representation to avoid this. If there are cases where truncating would remove relevant information, please speak up.

[hendrikmakait]

TIL: There is reprlib, which could be useful (https://docs.python.org/3/library/reprlib.html).