tweak variable move constructor #96

Job	Run time
busted (luajit-openresty, ubuntu-latest)	23s
busted (luajit-openresty, windows-latest)	1m 33s
busted (luajit-openresty, macos-latest)	1m 1s
busted (luajit-2.1.0-beta3, ubuntu-latest)	23s
busted (luajit-2.1.0-beta3, windows-latest)	2m 46s
busted (luajit-2.1.0-beta3, macos-latest)	49s
busted (luajit-git, ubuntu-latest)	23s
busted (luajit-git, windows-latest)	1m 43s
busted (luajit-git, macos-latest)	1m 30s
busted (5.4.6, ubuntu-latest)	23s
busted (5.4.6, windows-latest)	1m 42s
busted (5.4.6, macos-latest)	46s
busted (5.1.5, ubuntu-latest)	26s
busted (5.1.5, windows-latest)	1m 21s
busted (5.1.5, macos-latest)	44s
busted (5.3.6, ubuntu-latest)	23s
busted (5.3.6, windows-latest)	1m 44s
busted (5.3.6, macos-latest)	54s
busted (luajit-git, ubuntu-latest, rust)	39s
finish	3s
publish	0s
	19m 36s

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