fix(gnovm): improve error message for nil assignment in variable decl… #9128

Job	Run time
Run Main (autocounterd) / Go Build / generated	9s
Run Main (autocounterd) / Go Test / test	37s
Run Main (autocounterd) / Go Linter / lint	27s
Run Main (docker-integration) / Go Build / generated	9s
Run Main (docker-integration) / Go Linter / lint	9s
Run Main (docker-integration) / Go Test / test	14s
Run Main (genproto) / Go Build / generated	11s
Run Main (genproto) / Go Linter / lint	27s
Run Main (genproto) / Go Test / test	35s
Run Main (genstd) / Go Build / generated	12s
Run Main (genstd) / Go Linter / lint	14s
Run Main (genstd) / Go Test / test	23s
Run Main (goscan) / Go Build / generated	9s
Run Main (goscan) / Go Linter / lint	13s
Run Main (goscan) / Go Test / test	15s
Run Main (loop) / Go Build / generated	8s
Run Main (loop) / Go Linter / lint	25s
Run Main (loop) / Go Test / test	34s
	5m 31s

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