Increment version to 5.4.8.1 for testnet. #3095

Job	Run time
Lint	50s
ARM [GOAL install] [buster]	6m 58s
macOS 12 native [GOAL install] [GUI] [no depends]	10m 33s
Win32	8m 15s
Win64	11m 37s
i386 Linux [GOAL install] [focal]	7m 14s
x86_64 Linux [GOAL install] [GUI] [focal] [no depends]	16m 42s
x86_64 Linux [GOAL install] [GUI] [bionic] [no depends]	14m 44s
x86_64 Linux [ASan] [LSan] [UBSan] [integer] [jammy] [no depends]	14m 14s
macOS 10.14 [GOAL deploy] [GUI] [no tests] [focal]	9m 51s
	1h 40m 58s

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