Properly update retry_last_ts when hitting the maximum retry interval (#16156)

* Properly update retry_last_ts when hitting the maximum retry interval

This was broken in 1.87 when the maximum retry interval got changed from
almost infinite to a week (and made configurable).

fixes #16101

Signed-off-by: Nicolas Werner <nicolas.werner@hotmail.de>

* Add changelog

* Change fix + add test

* Add comment

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Signed-off-by: Nicolas Werner <nicolas.werner@hotmail.de>
Co-authored-by: Mathieu Velten <mathieuv@matrix.org>