Ensure normal weight math font face is consistent (#1774)

crates/typst-library/src/math/ctx.rs

@@ -258,7 +258,9 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
         self.local.set(TextElem::set_weight(if style.bold {
             FontWeight::BOLD
         } else {
-            FontWeight::REGULAR
+            // The normal weight is what we started with.
+            // It's 400 for CM Regular, 450 for CM Book.
+            self.font.info().variant.weight
         }));
         self.style = style;
     }

crates/typst/src/font/mod.rs

@@ -134,7 +134,7 @@ impl Hash for Font {
 
 impl Debug for Font {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        write!(f, "Font({})", self.info().family)
+        write!(f, "Font({},{:?})", self.info().family, self.info().variant)
     }
 }