The owner's address of MerkleAirdrop.sol contract is Deploy.s.sol any Ether sent to it would cause the transfer to revert without the implementation of receive function.
The low-lvl call in MerkleAirdrop:claimFees will revert because the owner account isn't capable of receiving Ether. The owner's address of MerkleAirdrop.sol is a contract Deploy.s.sol and this contract doesn't implement a function for handling plain Ether transfers.
The owner won't be able to claim the FEES generated during the airdrop session.
Manual review
Add a receive function in Deploy.s.sol or transfer the ownership of MerkleAirdrop.sol to an EOA.
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