promote-charm: doc-automation-disabled unexpectedly requires Discourse creds

[andrei-polukhin]

Dear team!

I am using the promote_charm.yaml GitHub workflow, but I have a weird experience using the doc-automation-disabled: true parameter. My expectation is that the Publish docs step is fully skipped, but it doesn't appear to be the case:

operator-workflows/.github/workflows/promote_charm.yaml

Lines 200 to 201 in 34f1737

	publish-docs:
	if: ${{ github.event.inputs.destination-channel }} == 'latest/stable'

Instead, this input is thrown into the dry_run parameter, which looks a bit weird to me:

operator-workflows/.github/workflows/promote_charm.yaml

Line 220 in 34f1737

dry_run: ${{ inputs.doc-automation-disabled }}

The problem with this approach is that I do not want any documentation to be published, which is clearly shown as the description to my parameter, but when running with the documentation disabled and w/o Discourse credentials, I get the following error in the GitHub workflow:

INFO:root:Base branch: main (commit e01531f185ba35cc35fbce909436923d6e69fc0c)
Traceback (most recent call last):
  File "/usr/src/app/main.py", line 257, in <module>
    main()
  File "/usr/src/app/main.py", line 240, in main
    assert main_checks(user_inputs=user_inputs)  # pylint: disable=no-value-for-parameter
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/app/main.py", line 170, in wrapper
    output = func(execute_cwd, *args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/app/main.py", line 224, in main_checks
    clients = get_clients(user_inputs, path)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/app/src/clients.py", line 38, in get_clients
    discourse=create_discourse(
              ^^^^^^^^^^^^^^^^^
  File "/usr/src/app/src/discourse.py", line 541, in create_discourse
    raise InputError(
src.exceptions.InputError: Invalid 'discourse_api_username' input, it must be non-empty, got api_username=''

Could we change the if condition for the Publish docs step so that it does not run on doc-automation-disabled: true? Here is my GitHub workflow file for posterity: https://github.com/canonical/pro-airgapped/blob/e01531f185ba35cc35fbce909436923d6e69fc0c/.github/workflows/charm-promotion.yml

Thank you very much in advance!