Brazil's Petrobras wants to buy stakes in African oil assets, mainly in Angola, Namibia and South Africa, to boost its reserves as it expects output to fall after 2030, a senior executive said on Wednesday.The Brazilian state energy firm is in talks with companies, including existing partners ExxonMobi, Shell and TotalEnergies, to buy a share of their African assets, Sylvia dos Anjos, the company's director for exploration and production…