Fix feedback form input width

UserActionRow relies on the box-sizing: border-box but does not set it
itself and width: 100% depends on the box-sizing. Auto width makes it
not dependent on box-sizing.

Bug: none
Change-Id: I58e80431d0049e4861b9b94fb0a74d2790925a3b
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6343234
Reviewed-by: Ergün Erdoğmuş <[email protected]>
Auto-Submit: Alex Rudenko <[email protected]>
Commit-Queue: Alex Rudenko <[email protected]>

Author: OrKoN

front_end/panels/ai_assistance/components/userActionRow.css

@@ -94,6 +94,7 @@
     height: var(--sys-size-11);
     padding: 0 var(--sys-size-5);
     background-color: var(--sys-color-surface3);
+    width: auto;
   }
 
   .feedback-input::placeholder {