For #21708 - Fixes missing header bottom border

The bottom gray border of the header item from the Inactive Tabs section was correctly set when collapsing or expanding said section, but not on init. So if the section was initialized collapsed the gray border would not be present.

app/src/main/java/org/mozilla/fenix/tabstray/browser/InactiveTabViewHolder.kt

@@ -38,6 +38,8 @@ sealed class InactiveTabViewHolder(itemView: View) : RecyclerView.ViewHolder(ite
             itemView.apply {
                 isActivated = InactiveTabsState.isExpanded
 
+                correctHeaderBorder(isActivated)
+
                 setOnClickListener {
                     val newState = !it.isActivated
 
@@ -46,10 +48,7 @@ sealed class InactiveTabViewHolder(itemView: View) : RecyclerView.ViewHolder(ite
                     it.isActivated = newState
                     binding.chevron.rotation = ROTATION_DEGREE
 
-                    // When the header is collapsed we use its bottom border instead of the footer's
+                    correctHeaderBorder(isActivated)
-                    binding.inactiveHeaderBorder.updatePadding(
-                        bottom = binding.root.context.dpToPx(if (it.isActivated) 0f else 1f)
-                    )
                 }
 
                 binding.delete.setOnClickListener {
@@ -58,6 +57,15 @@ sealed class InactiveTabViewHolder(itemView: View) : RecyclerView.ViewHolder(ite
             }
         }
 
+        /**
+         * When the header is collapsed we use its bottom border instead of the footer's
+         */
+        private fun correctHeaderBorder(isActivated: Boolean) {
+            binding.inactiveHeaderBorder.updatePadding(
+                bottom = binding.root.context.dpToPx(if (isActivated) 0f else 1f)
+            )
+        }
+
         companion object {
             const val LAYOUT_ID = R.layout.inactive_header_item
             private const val ROTATION_DEGREE = 180F