chore(styles): update signal icons (#6268)

## 📄 Description

This update the signal icons in light mode (a follow-up ticket will be
created for dark mode).

## 🚀 Demo


https://preview-6268--swisspost-design-system-next.netlify.app/?path=/docs/105e67d8-31e9-4d0b-87ff-685aba31fd4c--docs

---

## 📝 Checklist

- ✅ My code follows the style guidelines of this project
- 🛠️ I have performed a self-review of my own code
- 📄 I have made corresponding changes to the documentation
- ⚠️ My changes generate no new warnings or errors
- 🧪 I have added tests that prove my fix is effective or that my feature
works
- ✔️ New and existing unit tests pass locally with my changes

Author: alizedebray

.changeset/cold-snails-fall.md

@@ -0,0 +1,5 @@
+---
+'@swisspost/design-system-styles': patch
+---
+
+Updated the signal icons.