Merge rust-bitcoin/rust-bitcoincore-rpc#339: Upgrade `jsonrpc` to ver… #398

Job	Run time
Test - 1.56.1 toolchain (minimal)	2m 55s
Integration tests - stable toolchain (0.18.0)	53s
Test - 1.56.1 toolchain (recent)	2m 53s
Test - nightly toolchain (minimal)	46s
Integration tests - stable toolchain (0.18.1)	56s
Test - stable toolchain (minimal)	39s
Integration tests - stable toolchain (0.19.0.1)	1m 23s
Test - nightly toolchain (recent)	45s
Test - stable toolchain (recent)	45s
Integration tests - stable toolchain (0.19.1)	1m 1s
Integration tests - stable toolchain (0.20.0)	1m 4s
Integration tests - stable toolchain (0.20.1)	1m 6s
Integration tests - stable toolchain (0.21.0)	1m 26s
	16m 32s

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