cannot rebase a MR if approval is required

When MRs require approval before merge and the MR is not approved yet. The rebase button does not appear.

Note this button always appear when approval is not required to merge.

I'm not 100% sure, but I'd say this is a regression and before the button appeared also in this situation, which IMO is convenient. Also looking at this issue, I understand this is how it worked: #1494 (comment 50981901).