Do not display inlay hints as bold (#8283)

I think bold is the least fitting font weight for inlay hints, which
should be subtle hints and not, well, bold.

If someone feels strongly about this, I can revert, but only if we add
the ability to change this per theme.

Until then: beautiful, thin, subtle inlay hints!

Release Notes:

- Improved styling of inlay hints by not making them bold in the editor.


![screenshot-2024-02-23-17 30
29@2x](https://github.com/zed-industries/zed/assets/1185253/89c2a162-76bb-45cd-8b45-2a5bdf8ca87b)

assets/themes/gruvbox/gruvbox.json

@@ -482,7 +482,7 @@
         "hidden": "#998b78ff",
         "hidden.background": "#4c4642ff",
         "hidden.border": "#544c48ff",
-        "hint": "#8c957dff",
+        "hint": "#6a695bff",
         "hint.background": "#1e2321ff",
         "hint.border": "#303a36ff",
         "ignored": "#c5b597ff",