It's a present perfect passive. 'Have been' is the present perfect of the helping verb (be) and 'made' is the past participle of the main verb (make). We're using a present perfect aspect because we're talking about recent time. These mistakes have had an effect on the present moment. We're using a passive voice because we don't know or don't want to say who has made these mistakes. By making 'mistakes' the subject of the sentence we are emphasising the mistakes themselves rather than the person or the people who made them.

This is the Present Perfect Passive. We tend to use the passive voice to talk about actions and not the person who does the action. This can be because: 1. We don't know who did the action 2. The person who did the action is a secret 3. The person who did the action is not important (If it is done by many people for example). We are using the Present Perfect version of it because those mistakes are still relevant now. Either, 1. They happened recently, or 2 They happened a while ago but still have an impact on us now.