Fix if check before setting is_valid=true in validate.yml (Fixes #49)

[MelissaAutumn]

I believe this should work. From here: https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/evaluate-expressions-in-workflows-and-actions#success

Previously the conclusion wasn't returning the correct result even if the schema validation completed successfully. See here: https://github.com/thunderbird/thunderbird-notifications/actions/runs/12357823635/job/34487001239

Note: This ticket does not touch #21 which I just discovered now. It simply fixes the workflow to commit the json.

[MelissaAutumn]

Seems like that didn't do the trick.

[MelissaAutumn]

Okay fixed. It seems like it was evaluating {{0} == "true". I pushed the output to an env in that step and referenced the env in the if check.

Should we exit 1 if the "schema validation has failed" branch is true? I assume the validate.yml will already error out, but I guess we should add a guard against committing too.

[radishmouse]

Should we exit 1 if the "schema validation has failed" branch is true? I assume the validate.yml will already error out, but I guess we should add a guard against committing too.

I vote yes to exit 1 if the schema validation fails