Fix unverified_smart_contract function: add md5 of bytecode to the changeset

[vbaranov]

Motivation

An error like this on smart-contract verification with wrong data:

2022-04-12T13:51:39.560 application=block_scout_web request_id=FuUqcBSo6HEjK1cAADtS [error] Something went wrong while publishing the contract.{:error, #Ecto.Changeset<action: :insert, changes: %{address_hash: %Explorer.Chain.Hash{byte_count: 20, bytes: <<55, 208, 237, 37, 143, 55, 169, 102, 243, 59, 117, 181, 174, 116, 134, 145, 122, 10, 230, 20>>}, compiler_version: "0.8.13+commit.abaa5c0e", contract_source_code: "pragma solidity ^0.8.0; contract Example { }", is_vyper_contract: false, name: "Example", optimization: false, optimization_runs: 200}, errors: [contract_source_code: {"There was an error compiling your contract.", []}, contract_code_md5: {"can't be blank", [validation: :required]}], data: #Explorer.Chain.SmartContract<>, valid?: false>}

Changelog

add md5 of smart-contract's bytecode to the changeset

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
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