Fix: remove leftover block_on from `graphman chain change-shard` #10983

Job	Run time
Build in release mode	5m 39s
Subgraph Runner integration tests	3m 8s
Run unit tests	2m 43s
Check rustfmt style	29s
Run integration tests	4m 43s
Clippy linting	5m 27s
	22m 9s

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