Update `openapi.json` file path in `generate_api_docs.yaml`

[pavithraes]

Description

This pull request adds the complete file path to the openapi.json file generate_api_docs.yaml GitHub Action.

This path is used in a git add in the action. The incomplete path results in Error: Error: fatal: pathspec 'openapi.json' did not match any files

Thanks for surfacing the issue, @trallard!

Pull request checklist

• [ ] Did you test this change locally?
• [ ] Did you update the documentation (if required)?
• [ ] Did you add/update relevant tests for this change (if required)?

Additional information

xref: #782

How to test

I don't think there is a quick way to test this, besides testing on a fork.

[netlify[bot]]

✅ Deploy Preview for conda-store canceled.

Name	Link
🔨 Latest commit	cc68a45769ddd8740a7bf07af52115f15f1dfd6c
🔍 Latest deploy log	https://app.netlify.com/sites/conda-store/deploys/66bcce37058e1f00084a62fb