President Joe Biden seemed to struggle to remember the name of his own defense secretary amid increased concerns over the aging, COVID-stricken leader’s cognitive decline. The 81-year-old POTUS’ latest gaffe came as he boasted about his record of appointing Black men to important positions within his administration in an interview with BET on Wednesday, RadarOnline.com can reveal. Biden said: “It’s all about treating people with dignity. Look at the heat I’m getting because I named a — the, uh — secretary of defense, a Black man. I named [Supreme Court Associate Justice] Ketanji Brown [Jackson…