fix(logo): set width to width of largest logo (#10652)

We have three logos: mdn, mdn plus, mdn web docs.

These have different width, which causes the menu to
jump when navigating between these parts of MDN.

By setting a fixed width, we avoid these jumps.

client/src/ui/atoms/logo/index.scss

@@ -3,6 +3,8 @@
 .logo {
   align-items: center;
   display: flex;
+  // Width of largest logo ("mdn web docs").
+  width: 160px;
 
   svg {
     height: 1.5rem;