test: fix off-by-one in dynamically_add_masternode #113

Job	Run time
Build Image	28s
Build Dependencies (arm-linux, arm-linux-gnueabihf)	1m 8s
Build Dependencies (linux64, x86_64-pc-linux-gnu)	1m 9s
Build (arm-linux, arm-linux-gnueabihf, arm-linux)	4m 22s
Build (linux64, x86_64-pc-linux-gnu, linux64)	6m 26s
Build (linux64_tsan, x86_64-pc-linux-gnu, linux64)	11m 29s
Build (linux64_ubsan, x86_64-pc-linux-gnu, linux64)	7m 50s
Build (linux64_fuzz, x86_64-pc-linux-gnu, linux64)	14m 53s
Build (linux64_cxx20, x86_64-pc-linux-gnu, linux64)	7m 17s
Build (linux64_sqlite, x86_64-pc-linux-gnu, linux64)	7m 8s
Build (linux64_nowallet, x86_64-pc-linux-gnu, linux64)	7m 36s
	1h 9m 46s

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