[pallet_contracts] Increase the weight of the deposit_event host function to...

[pallet_contracts] Increase the weight of the deposit_event host function to limit the memory used by events. (#4973)

This PR updates the weight of the `deposit_event` host function by
adding
a fixed ref_time of 60,000 picoseconds per byte. Given a block time of 2
seconds
and this specified ref_time, the total allocation size is 32MB.

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Co-authored-by: Alexander Theißen <alex.theissen@me.com>