vm.install-debian: increase default RAM for Bullseye

With only 384M, debian-11.0.0-amd64-netinst.iso fails to initialize
the network interface.

slapos/recipe/vm.py

@@ -305,7 +305,7 @@ class InstallDebianRecipe(BaseRecipe):
           for k, v in p.items())))
 
         vm = join(location, dist + '.img')
-        args = self.getQemuBasicArgs(dist, 384, unsafe=True)
+        args = self.getQemuBasicArgs(dist, 512, unsafe=True)
         open_flags = os.O_CREAT | os.O_EXCL | os.O_WRONLY
         fd = os.open(vm, open_flags, 0o666)
         try: