ci: split out `multiprocess` linting to a separate step on Actions #336

Job	Run time
Build slim container / Build container	22s
Build container / Build container	21s
x86_64-pc-linux-gnu / Build depends	1m 3s
arm-linux-gnueabihf / Build depends	56s
x86_64-pc-linux-gnu_multiprocess / Build depends	57s
x86_64-apple-darwin / Build depends	59s
x86_64-pc-linux-gnu_nowallet / Build depends	54s
x86_64-w64-mingw32 / Build depends	1m 1s
linux64_nowallet-build / Build source	6m 22s
arm-linux-build / Build source	3m 51s
linux64_tsan-build / Build source	6m 49s
linux64_multiprocess-build / Build source	6m 49s
mac-build / Build source	3m 40s
win64-build / Build source	6m 40s
linux64_sqlite-build / Build source	6m 27s
linux64_ubsan-build / Build source	6m 40s
linux64_fuzz-build / Build source	6m 39s
linux64-build / Build source	6m 14s
linux64_nowallet-test / Test source	20s
linux64-test / Test source	15s
linux64_sqlite-test / Test source	1s
linux64_multiprocess-test	1s
linux64_tsan-test	1s
linux64_ubsan-test	1s
	1h 7m 23s

Provide feedback