What is the ruling on the financial increase I received for working the Ramadan shift, given that I was on annual leave and it was requested for me as a bonus?

If the shift allowance is granted to those who worked in Sha'ban according to the company's system, then there is no harm in taking it, even if it is named 'Ramadan shift allowance'. However, if the allowance is specifically for those who worked in Ramadan, then it is not permissible for you to take it in exchange for your work in Sha'ban, unless your manager is authorized by the company to grant this allowance to those who did not work in Ramadan, in which case it becomes permissible for you to take it.