chore: replaced checkbox icon (#1637)

Author: lukasvinclav

src/unfold/static/unfold/css/styles.css

@@ -176,7 +176,7 @@
     "focus:outline-offset-2",
     "focus:outline-primary-500",
     "after:absolute",
-    "after:content-['done']",
+    r"after:content-['check\_small']",
     "after:flex!",
     "after:h-4",
     "after:items-center",
@@ -185,7 +185,6 @@
     "after:material-symbols-outlined",
     "after:-ml-px",
     "after:-mt-px",
-    "after:text-sm!",
     "after:text-white",
     "after:transition-all",
     "after:w-4",