ui: Reduce icons stroke width (#36361)

After redesigning all Zed icons
(https://github.com/zed-industries/zed/pull/35856), it felt like using
1.5 for stroke width didn't really flow well with the default typeface
default font weight. Reducing it to 1.2 makes the UI much sharper, less
burry, and more cohesive overall.

Release Notes:

- N/A

assets/icons/check_circle.svg

@@ -1,4 +1,4 @@
 <svg width="16" height="16" viewBox="0 0 16 16" fill="none" xmlns="http://www.w3.org/2000/svg">
-<path d="M5.94873 9.02564L7.48722 10.0513L10.0514 6.46149" stroke="black" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
-<path d="M8 14C11.3137 14 14 11.3137 14 8C14 4.68629 11.3137 2 8 2C4.68629 2 2 4.68629 2 8C2 11.3137 4.68629 14 8 14Z" stroke="black" stroke-width="1.5"/>
+<path d="M5.94873 9.02564L7.48722 10.0513L10.0514 6.46149" stroke="black" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"/>
+<path d="M8 14C11.3137 14 14 11.3137 14 8C14 4.68629 11.3137 2 8 2C4.68629 2 2 4.68629 2 8C2 11.3137 4.68629 14 8 14Z" stroke="black" stroke-width="1.2"/>
 </svg>