Bump github.com/grpc-ecosystem/grpc-gateway/v2 from 2.15.2 to 2.18.1 in /exposer #648

Job	Run time
pr-test (one-chain-custom-scripts.yaml)	4m 37s
pr-test (one-chain.yaml)	4m 49s
pr-test (one-custom-chain.yaml)	3m 56s
pr-test (multi-validator.yaml)	4m 0s
pr-test (simapp.yaml)	5m 27s
pr-test (one-chain-starship-faucet.yaml)	4m 24s
pr-test (multi-validator-starship-faucet.yaml)	3m 30s
pr-test (one-chain-cometmock.yaml)	4m 0s
	34m 43s

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