add unit tests for `action/protocol/staking/protocol.go`

[saitofun]

What would you like to be added

add unit tests for action/protocol/staking/protocol.go

• Add unit tests to cover L517
• Add unit tests to cover L529-L530
• Add unit tests to cover L541-L543
• Add unit tests to cover L546
• Add unit tests to cover L548
• Add unit tests to cover L550
• Add unit tests to cover L552
• Add unit tests to cover L554
• Add unit tests to cover L556
• Add unit tests to cover L558
• Add unit tests to cover L560-L574