fix(gnovm): improve error message for nil assignment in variable decl… #9157

Job	Run time
Run Main (autocounterd) / Go Build / generated	9s
Run Main (autocounterd) / Go Linter / lint	46s
Run Main (autocounterd) / Go Test / test	37s
Run Main (docker-integration) / Go Build / generated	6s
Run Main (docker-integration) / Go Linter / lint	13s
Run Main (docker-integration) / Go Test / test	11s
Run Main (genproto) / Go Build / generated	12s
Run Main (genproto) / Go Linter / lint	30s
Run Main (genproto) / Go Test / test	27s
Run Main (genstd) / Go Build / generated	15s
Run Main (genstd) / Go Linter / lint	19s
Run Main (genstd) / Go Test / test	20s
Run Main (goscan) / Go Build / generated	8s
Run Main (goscan) / Go Linter / lint	15s
Run Main (goscan) / Go Test / test	10s
Run Main (loop) / Go Build / generated	20s
Run Main (loop) / Go Linter / lint	25s
Run Main (loop) / Go Test / test	29s
	5m 52s

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