fix(gnovm): improve error message for nil assignment in variable decl… #9129

Job	Run time
Run Main (autocounterd) / Go Linter / lint	26s
Run Main (autocounterd) / Go Build / generated	15s
Run Main (autocounterd) / Go Test / test	26s
Run Main (docker-integration) / Go Build / generated	10s
Run Main (docker-integration) / Go Linter / lint	14s
Run Main (docker-integration) / Go Test / test	12s
Run Main (genproto) / Go Build / generated	7s
Run Main (genproto) / Go Linter / lint	20s
Run Main (genproto) / Go Test / test	31s
Run Main (genstd) / Go Build / generated	9s
Run Main (genstd) / Go Linter / lint	21s
Run Main (genstd) / Go Test / test	26s
Run Main (goscan) / Go Build / generated	10s
Run Main (goscan) / Go Linter / lint	12s
Run Main (goscan) / Go Test / test	17s
Run Main (loop) / Go Build / generated	15s
Run Main (loop) / Go Linter / lint	32s
Run Main (loop) / Go Test / test	35s
	5m 38s

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