Bump flatted from 3.2.7 to 3.4.2 in /dash/dash-renderer #984

Job	Run time
Detect Relevant Path Changes	5s
Build Dash Package	3m 4s
Typing Tests	2m 38s
Run Background & Async Callback Tests (Python 3.12)	10m 59s
Table Unit/Lint Tests (Python 3.12)	1m 35s
Run Background & Async Callback Tests (Python 3.9)	10m 43s
Table Server Tests (Group 3)	13m 51s
Table Server Tests (Group 1)	14m 49s
Table Server Tests (Group 2)	14m 34s
	1h 12m 18s

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