Copy files with github-action

I am trying to write a GitHub action that makes a copy of a file in my repo into a different subdir in the repo. This is my dir structure (before the file is copied)

my_project
  |_ .github
  |     |_ workflows
  |          |_ run_tests.yml
  |          |_ copy_file.yml
  |_ tests
  |    |_ testthat
  |         |_ test1.R
  |         |_ test2.R
  |_ my_file.json
  |_ copyfile.sh

This is what I want my file structure to be after the file is copied

my_project
  |_ .github
  |     |_ workflows
  |          |_ run_tests.yml
  |          |_ copy_file.yml
  |_ tests
  |    |_ testthat
  |    |    |_ test1.R
  |    |    |_ test2.R
  |    |_ copy_of_my_file.json
  |_ my_file.json
  |_ copyfile.sh

So basically, my GitHub action should make a copy of my_file.json named copy_of_my_file.json and place it inside the tests sub dir. I've built a bash script with the following

#!/bin/bash
cp my_file.json tests/copy_of_my_file.json

Locally, I run chmod u+x copyfile.sh and then bash copyfile.sh and the file is indeed copied. My copy_file.yml workflow is as follows:

name: Copy my_file.json to tests subdirectory
on: [push, pull_request, workflow_dispatch]
jobs:
  run:
    runs-on: [ubuntu-latest]
    steps:
    - name: Checkout ️
      uses: actions/checkout@v2

    - name: Make copy of my_file.json 
      run: |
        chmod u+x "${GITHUB_WORKSPACE}/copyfile.sh"
        bash "${GITHUB_WORKSPACE}/copyfile.sh"

The action runs with no errors, but the file doesn't get copied. I tried other actions from the GitHub Marketplace with no luck. I also tried changing the action's run to simply cp my_file.json tests/copy_of_my_file.json but it doesn't work either.