Skip ring of experts all gather when EP = 1

[Shuwen-Fang]

Description

Currently runs error out when EP = 1 and ring of experts is used, fix by skipping all gather when EP = 1. This PR updates the logic to only all gather when EP > 1.

Tests

CI tests

Checklist

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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