fix(vertical-nav): add missing type attribute to close button (#770)

## PR Checklist

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- [ ] Tests for the changes have been added (for bug fixes / features)
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## PR Type

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- [x] Bugfix
- [ ] Feature
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## What is the current behavior?

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## What is the new behavior?

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## Other information

projects/angular/src/layout/vertical-nav/vertical-nav.html

@@ -23,6 +23,7 @@
 <div class="nav-content">
  <ng-content></ng-content>
  <button
+ type="button"
  (click)="collapsed = false"
  class="nav-btn"
  aria-hidden="true"