Add gcov #53

Job	Run time
busted (luajit-openresty, ubuntu-latest)	59s
busted (luajit-openresty, windows-latest)	1m 56s
busted (luajit-openresty, macos-latest)	1m 5s
busted (luajit-2.1.0-beta3, ubuntu-latest)	50s
busted (luajit-2.1.0-beta3, windows-latest)	1m 35s
busted (luajit-2.1.0-beta3, macos-latest)	49s
busted (luajit-git, ubuntu-latest)	36s
busted (luajit-git, windows-latest)	1m 39s
busted (luajit-git, macos-latest)	52s
busted (5.4.6, ubuntu-latest)	30s
busted (5.4.6, windows-latest)	1m 20s
busted (5.4.6, macos-latest)	59s
busted (5.1.5, ubuntu-latest)	35s
busted (5.1.5, windows-latest)	1m 47s
busted (5.1.5, macos-latest)	42s
busted (5.3.6, ubuntu-latest)	35s
busted (5.3.6, windows-latest)	1m 43s
busted (5.3.6, macos-latest)	40s
finish	6s
	19m 18s

Provide feedback