fix: use correct index as shadowstack slot key (#2719) #4498

Job	Run time
Check	4s
Compiler (ubuntu, node current)	3m 35s
Compiler (ubuntu, node lts_latest)	3m 4s
Compiler (macos, node current)	4m 43s
Compiler (macos, node lts_latest)	4m 36s
Compiler (windows, node current)	4m 18s
Compiler (windows, node lts_latest)	4m 0s
Features	5m 43s
Loader	37s
Runtimes	57s
Bootstrap (debug)	9m 46s
Bootstrap (release)	8m 31s
	49m 54s

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