Hopefully reusable workflow agrees to support ${{inputs. XXX}} expression parameter passing

Describe the enhancement
I wanted to pass the parameters of the workflow_dispatch input in a reusable workflow,
and with ${{inputs.username}} expression, the value could not be read and without an error message.

But if using ${{github.event.inputs.username}} it works fine, I don't know why.
The official documentation does not detail the difference between the two and which to use in reusable workflows

Code Snippet

name: Caller

on:
  workflow_dispatch:
    inputs:
      username:
        type: string
        description: 'username'
        required: false
        default: 'john-doe'
        
jobs:
  Test-1:
      uses: ./.github/workflows/test_1.yml
      with:
        username: ${{ inputs.username }}       #${{ github.event.inputs.username }}
      secrets: inherit

name: Executor

on:
  push:
  workflow_call:
    inputs:
      username:
        type: string
        description: 'A username passed from the caller workflow'
        default: 'john-doe'
        required: false
        
      
jobs:
  Test-1:
    runs-on: ubuntu-latest
    steps:
      - name: Print the input name to STDOUT
        run: echo The username is ${{ inputs.username }}

Additional information
Add any other context about the feature here.

NOTE: if the feature request has been agreed upon then the assignee will create an ADR. See docs/adrs/README.md

Start by comparing the workflow_dispatch and workflow_call input examples in the issue, then read docs/adrs/README.md for the repository's process for agreed feature requests. Determine the expected behavior and documentation for passing inputs through a reusable workflow, and confirm the result using the shown Caller and Executor workflows.