feat(coverage): Add back coverage support for `txtar` #3457

Job	Run time
setup	3s
Run Main (gnodev) / Go Build / generated	11s
Run Main (gnodev) / Go Linter / lint	39s
Run Main (gnodev) / Go Test / test	1m 6s
Run Main (gnofaucet) / Go Linter / lint	32s
Run Main (gnofaucet) / Go Test / test	34s
Run Main (gnofaucet) / Go Build / generated	10s
Run Main (gnokeykc) / Go Build / generated	12s
Run Main (gnokeykc) / Go Linter / lint	33s
Run Main (gnokeykc) / Go Test / test	40s
Run Main (gnomd) / Go Build / generated	6s
Run Main (gnomd) / Go Linter / lint	34s
Run Main (gnomd) / Go Test / test	27s
	5m 47s

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