[Fix #1356] Enhance `Rails/DuplicateAssociation` to handle alias #524

Job	Run time
Check documentation syntax	10s
Spec - JRuby	1m 39s
Check the oldest supported RuboCop version	28s
Spec - 2.7	28s
Prism	32s
Spec - 3.0	22s
Spec - 3.1	32s
Spec - 3.2	13s
Spec - 3.3	17s
Spec - 3.4	17s
Spec - head	15s
	5m 13s

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