Added security considerations and backwards compatibility texts for EIP-5023

[yaruno]

When opening a pull request to submit a new EIP, please use the suggested template: https://github.com/ethereum/EIPs/blob/master/eip-template.md

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[eth-bot]

All tests passed; auto-merging...

(pass) eip-5023.md

classification
updateEIP

• passed!