Fix equation resizing when adding the equation number

[Leedehai]

#set math.equation(numbering: "1")
#grid(
  columns: 4 * (1fr,), column-gutter: 3 * (2pt,), row-gutter: 2pt, align: horizon,
  [
    #set math.equation(number-align: horizon)
    #box($ - - \ a \ sum $, fill: silver)
  ],
  [
    #set math.equation(number-align: bottom)
    #box($ - - \ a \ sum $, fill: silver)
  ],
  [
    #set math.equation(number-align: horizon)
    #box($ sum \ a \ - - $, fill: silver)
  ],
  [
    #set math.equation(number-align: top)
    #box($ sum \ a \ - - $, fill: silver)
  ],
)

Before:

After:

[laurmaedje]

Thank you!