Add `UnusedVariableNames` missing checks #71

Job	Run time
all triggers are looked up and confirmed	22s
resulting issues are still the same (optional)	1m 10s
used mix format	32s
compiling deps shows no compiler warnings (optional)	25s
tested that for each check all params are covered by tests	23s
tested that for each check there is at least one trigger assertion	19s
	3m 11s

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