onboarding: Add proper icon for action (#35241)

This change updates one icon within the onboarding flow to the indended
icon for that entry.

Release Notes:

- N/A

assets/icons/cloud_download.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-cloud-download-icon lucide-cloud-download"><path d="M12 13v8l-4-4"/><path d="m12 21 4-4"/><path d="M4.393 15.269A7 7 0 1 1 15.71 8h1.79a4.5 4.5 0 0 1 2.436 8.284"/></svg>

crates/icons/src/icons.rs

@@ -71,6 +71,7 @@ pub enum IconName {
     CircleHelp,
     Close,
     Cloud,
+    CloudDownload,
     Code,
     Cog,
     Command,

crates/onboarding/src/welcome.rs

@@ -32,8 +32,7 @@ const CONTENT: (Section<4>, Section<3>) = (
                 action: &Open,
             },
             SectionEntry {
-                // TODO: use proper icon
-                icon: IconName::Download,
+                icon: IconName::CloudDownload,
                 title: "Clone a Repo",
                 // TODO: use proper action
                 action: &NoAction,