Description:
The label addition is not atomic and there is a small time window after opening a PR where the action will unexpectedly remove user-added labels. Example from here:

I guess the API flow is like this:

• Labeler does a GET labels request
• User changes labels (which invalidates the labels seen in the GET)
• Labeler does a PUT labels request with previously seen labels, reverting the user's changes

Action version:
v5

Platform:

• All

Runner type:

• All

Repro steps:

1. Have a simple labeler action with this config
2. Open a PR
3. Immediatly set some labels on the PR
4. If the timing is right, the labeler will unexpectedly remove the user-added labels

Expected behavior:
The action should atomically update the labels or at least never removing labels it does not have in its config.

Actual behavior:
The action will remove user-set labels when set within a certain time window.