Use multiple API keys for pre-merge testing

[surajkumar]

When running the pre-commit Github Action we are sometimes rate limited when there are too many concurrent actions running.

Instead what we can implement to mitigate this round robin the secrets.

Here's an example of what we can do:

Add a select key step:

- name: Select API key
  id: select_api_key
  run: echo "::set-output name=api_key::${{ secrets.API_KEY_$(( github.run_number % NUM_KEYS + 1 )) }}"

To use the key: API_KEY: ${{ steps.select_api_key.outputs.api_key }}

We would need to create multiple discord API keys for this work and create them as API_KEY_1, API_KEY_2, API_KEY_3

[surajkumar]

No longer needed - this has been fixed with parsing the rate limit headers