Limit Good First Issues to a single assignee (#33543)
### Details:
- GFI assignment should limit the amount of assignees to 1
- Current behavior causes confusion where multiple people are working on
a single issue in parallel, ex.
https://github.com/openvinotoolkit/openvino/issues/32725
- Tested in https://github.com/p-wysocki/openvino/issues/155
### Tickets:
- N/A
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Signed-off-by: p-wysocki <przemyslaw.wysocki@intel.com>
