miniscript: add an unit test for substitute_raw_pkh() #1998

Job	Run time
Docs - stable toolchain (recent)	43s
Bench - nightly toolchain (recent)	1m 36s
Embedded	1m 30s
Docs - nightly toolchain (recent)	28s
Format - nightly toolchain	13s
Integration tests - stable toolchain (26_0)	1m 5s
Lint - nightly toolchain (recent)	30s
Integration tests - stable toolchain (25_2)	59s
Test - 1.63.0 toolchain (minimal)	0s
Integration tests - stable toolchain (25_1)	1m 16s
Test - nightly toolchain (minimal)	0s
Test - 1.63.0 toolchain (recent)	0s
Integration tests - stable toolchain (25_0)	1m 16s
Test - stable toolchain (minimal)	0s
Test - nightly toolchain (recent)	0s
Integration tests - stable toolchain (24_2)	51s
Test - stable toolchain (recent)	0s
Integration tests - stable toolchain (24_1)	49s
Integration tests - stable toolchain (24_0_1)	59s
Integration tests - stable toolchain (23_2)	53s
Integration tests - stable toolchain (23_1)	59s
Integration tests - stable toolchain (23_0)	1m 14s
Integration tests - stable toolchain (22_1)	54s
Integration tests - stable toolchain (22_0)	1m 5s
Integration tests - stable toolchain (0_21_2)	49s
Integration tests - stable toolchain (0_20_2)	48s
Integration tests - stable toolchain (0_19_1)	1m 6s
Integration tests - stable toolchain (0_18_1)	58s
Integration tests - stable toolchain (0_17_1)	58s
	21m 59s

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