ci: install busted to run lua tests #53

Job	Run time
build (ubuntu-latest)	2m 58s
build (ubuntu-latest, --disable-curses)	2m 46s
build (ubuntu-latest, --disable-lua)	2m 36s
build (ubuntu-latest, --disable-tre)	2m 44s
build (ubuntu-latest, --disable-selinux)	2m 50s
build (ubuntu-latest, --disable-acl)	2m 47s
build (ubuntu-latest, --disable-help)	2m 43s
build (ubuntu-20.04)	2m 54s
build (ubuntu-20.04, --disable-curses)	2m 54s
build (ubuntu-20.04, --disable-lua)	2m 40s
build (ubuntu-20.04, --disable-tre)	3m 5s
build (ubuntu-20.04, --disable-selinux)	2m 47s
build (ubuntu-20.04, --disable-acl)	2m 53s
build (ubuntu-20.04, --disable-help)	2m 47s
	39m 24s

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