fix(build): remove leftover code in action that labels issues on merge

[dreamorosi]

Description of your changes

At the moment, the workflow that is run every time a PR is merged attempts to label the issue related to that PR with a pending-release tag, to inform the person opening the issue that a change will be released soon.

At the moment the script that is run during this action has a bug coming from a leftover version of the script that makes it fail.

This PR aims at fixing the issue.

How to verify this change

Observe the result of the "On PR Merge" workflow at the next PR merged.

Related issues, RFCs

Issue number: #1076

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• My changes generate no new warnings
• The code coverage hasn't decreased
• New and existing unit tests pass locally and in Github Actions
• The PR title follows the conventional commit semantics

Breaking change checklist

N/A

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