Use timezone aware objects for RepositoryData.last_fetched #3955

Job	Run time
Preflight	1s
With hassfest	1m 6s
Check integration hacs/integration with HACS Action (local)	1m 12s
With HACS Action	23s
Check plugin piitaya/lovelace-mushroom with HACS Action (local)	1m 8s
Check integration hacs/integration with HACS data generation	39s
Check plugin piitaya/lovelace-mushroom with HACS data generation	37s
With Home Assistant stable	1m 25s
With Home Assistant beta	1m 26s
With Home Assistant dev	1m 27s
With Home Assistant 2023.6.0	1m 16s
Trigger Discord notification when jobs fail	0s
	10m 40s

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