themes: Fix Ayu theme comment colors (#39131)

Closes https://github.com/zed-industries/zed/issues/39122

Currently comment colors in Ayu theme do not work as expected and hard
to differentiate. In my understanding something is really wrong how zed
interprets rgba hex color codes, for example:

|  #5c677300 | #5c6773ff |
| ------------- | ---------- |
| <img width="134" height="38" alt="image"
src="https://github.com/user-attachments/assets/c9f1f618-958e-4fe9-a44a-636681d2f418"
/> | <img width="117" height="32" alt="image"
src="https://github.com/user-attachments/assets/78eac6b3-aecd-4be1-83d4-42590604c3a6"
/> |

This PR works around this by using comment color codes from
[ayu-vim](https://github.com/ayu-theme/ayu-vim). Maybe I am not
understanding how RGBA works, but in my opinion underlying issue should
be solved.

Release Notes:

- N/A

assets/themes/ayu/ayu.json

@@ -192,7 +192,7 @@
             "font_weight": null
           },
           "comment": {
-            "color": "#abb5be8c",
+            "color": "#5c6773ff",
             "font_style": null,
             "font_weight": null
           },
@@ -583,7 +583,7 @@
             "font_weight": null
           },
           "comment": {
-            "color": "#787b8099",
+            "color": "#abb0b6ff",
             "font_style": null,
             "font_weight": null
           },
@@ -974,7 +974,7 @@
             "font_weight": null
           },
           "comment": {
-            "color": "#b8cfe680",
+            "color": "#5c6773ff",
             "font_style": null,
             "font_weight": null
           },