Remove ! from todo!() in comments (#8643)

This practice makes it difficult to locate todo!s in my code when I'm
working. Let's take out the bang if we want to keep doing this.

Release Notes:

- N/A

crates/gpui/src/style.rs

@@ -208,7 +208,7 @@ impl Default for TextStyle {
     fn default() -> Self {
         TextStyle {
             color: black(),
-            // todo!(linux) make this configurable or choose better default
+            // todo(linux) make this configurable or choose better default
             font_family: if cfg!(target_os = "linux") {
                 "FreeMono".into()
             } else {