Add port to custom build

Author: Neradoc

.github/workflows/build-board-custom.yml

@@ -3,6 +3,10 @@ name: Build board (custom)
 on:
   workflow_dispatch:
     inputs:
+      port:
+        description: 'Port: Found in ports/[port]'
+        required: true
+        type: string
       board:
         description: 'Board: Found in ports/*/boards/[board_id]'
         required: true