CI: Cleanup flatpak-builder-lint action

[tytan652]

Description

• Replace jq usage with the new --gha-format option
• Remove unused workingDirectory input (was not removed alongside the replacement of a git clone with in-container pre-install)

Motivation and Context

Was on my list of TODO about Flatpak stuff

How Has This Been Tested?

This PR is the test

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[PatTheMav]

As path can be an absolute path but also potentially a relative path (that's the way it's used in the publish workflow right now), it needs to be relative to something.

The action cannot assume that the current working directory of the workflow that invoked it is actually the workspace directory or the root directory of a checkout, thus why this argument exists and uses the workspace as its default value.

This way the action by default establishes the state it needs to succeed and it also doesn't leak this requirement back into the workflow, which might need an entirely different working directory or might want to run the action for a secondary checkout created by the workflow itself.

---

The description should be updated of course, because it's not valid (it'd be more correct to say "Working directory to run flatpak-builder-lint from").

[tytan652]

workingDirectory is unused, there is nothing that uses it since a while and was meant as a destination to clone a third-party tool.

And this PR does not touch path at all, so I'm more on the side to consider this review out of scope.

Edit: Also the action has a hard deps on the container image used by Flatpak CIs.

[PatTheMav]

The working directory is used every time the action is invoked because it has a safe default value.

When flatpak-builder-lint is invoked with the path build-aux/com.obsproject.Studio.json (as happens in the publish workflow), then the path needs to point to a valid file.

If the calling workflow sets its working directory to some other path than the workspace, then the action would fail with these changes:

some_job:
  defaults:
    run:
      working-directory: <somewhere outside the checkout>
    steps:
      - name: Validate Flatpak manifest
        uses: ./.github/actions/flatpak-builder-lint
        with:
          artifact: manifest
          path: build-aux/com.obsproject.Studio.json

Because <somewhere outside the checkout>/build-aux/com.obsproject.Studio.json will not point to a valid file because of this change.

Otherwise the GitHub workspace would have been used as the default working directory, which is set for each step and thus the path would point to a valid file again. The actions are designed to work by default even if a workflow "forgot" that it has changed the working directory.

[Fenrirthviti]

While I understand the justification that the current use case may not directly benefit from defining workingDirectory here, it is considered best practice and all of our other updated actions use this paradigm. Since the runner images, or the checkout method, may change in the future this feels safe to still include as it doesn't harm anything.

Additionally, if you are removing something in a PR, and someone disagrees with that removal, stating their review is "out of scope" for your change is not really an acceptable comment just because you don't agree with them. The review is absolutely within scope; you're deleting something and someone is explaining why it shouldn't be deleted. That's about as in-scope of a review as it could possibly get. Please be mindful in the future, as those kinds of comments come across as dismissive.