Beer is about 95% water, so it's not that important to worry about the alcohol's boiling point— you can pretty much say that the beer will boil at 100ºC and ignore the alcohol. An oven is an enclosed space, and when you're cooking stuff with water in it (i.e. most foods) the relative humidity of the oven quickly reaches 100%, which means the air can hold no more water vapor. At that point, while the beer may be evaporating slightly, it condenses back into the bowl.

Beer is about 95% water, so it's not that important to worry about the alcohol's boiling point— you can pretty much say that the beer will boil at 100ºC and ignore the alcohol. An oven is an enclosed space, and when you're cooking stuff with water in it (i.e. most foods) the relative humidity of the oven quickly reaches 100%, which means the air can hold no more water vapor. At that point, while the beer may be evaporating slightly, it condenses back into the bowl.

Note that when you open the oven, the beer may start bubbling and boiling as the drier air from the room rushes in, allowing more liquid to evaporate.