Issue sending file created within workflow script

[BatMiles]

My workflow runs a python script which creates and writes to a log file. This file should be 'accessible in the container the action is running in' since it's created in a script in the workflow, but trying to send it via SLACK_FILE_UPLOAD so far hasn't worked. I'm no longer getting an error, but the file isn't showing up with the Slack notification.

pared-down version of the action:

name: "Scan Sponsored URLs"

on:
  push:
    branches:
      - "sponsored-urls-workflow"
  schedule:
    - cron: "0 0 * * 1"

jobs:
  scan:
    name: Make file
    runs-on: ubuntu-latest

    steps:
      - name: Checkout
        uses: actions/checkout@v4

      - name: setup python
        uses: actions/setup-python@v2
        with:
          python-version: 3.8

      - name: Install dependencies
        working-directory: ansible/scanner/
        run: |
          python -m pip install --upgrade pip
          if [ -f requirements.txt ]; then pip install -r requirements.txt; fi

      - name: execute py script # run file
        working-directory: ansible/scanner/
        run: |
          python scan.py

      - name: Slack Notification
        uses: rtCamp/action-slack-notify@v2
        env:
          SLACK_CHANNEL: **
          SLACK_COLOR: ${{ job.status }}
          SLACK_MESSAGE: **
          SLACK_TITLE: **
          SLACK_USERNAME:**
          SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK }}
          SLACK_TOKEN: ${{ secrets.SLACK_TOKEN }}
          SLACK_FILE_UPLOAD: 'ansible/scanner/output.txt'

pared-down scan.py (filepath is ansible/scanner/scan.py

file = open("output.txt", "x")
file.write('Success')