[Bug] `metropolis` theme doesn't allow us to align slide body

[tapyu]

In

#import "@preview/polylux:0.3.1": *
#import themes.metropolis: *

#show: metropolis-theme.with()
#set text(font: "Fira Sans", weight: "light", size: 20pt)
#slide(title: "Slide title")[

  #set align(top+left)
  A slide with some maths:
  $ x_(n+1) = (x_n + a/x_n) / 2 $

  #lorem(2)
]

For some reason, metropolis doesn't allow us to align the slide text body as #set align(top+left) does nothing. This is quite restrictive and should be fixed.