Make Ownable2Step.acceptOwnership virtual

[Amxx]

Ownable2Step.acceptOwnership is currently external non virtual. This prevents overriding the function.

IMO there are usecases where overriding this function is necessary. For example:

    uint256 public deadline;

    function transferOwnership(address newOwner) public virtual override {
        super.transferOwnership(newOwner); // this is onlyOwner
        deadline = block.timestamp + 2 days;
    }

    function acceptOwnership() public virtual override {
        require(deadline <= block.timestamp);
        delete deadline;
        super.acceptOwnership();
    }

PR Checklist

• Changelog entry

[frangio]

LGTM

[frangio]

👇 Missing changelog.