chore: remove extra slash when locating LuaJIT binary #16987

Job	Run time
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/plugin/[a-k]*)	36m 24s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/plugin/[l-z]*)	36m 25s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/admin t/cli t/config-center-yaml...	27m 8s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/node t/pubsub t/router t/script ...	26m 33s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/plugin/[a-k]*)	35m 25s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/plugin/[l-z]*)	38m 28s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/admin t/cli t/config-center-yaml t/cont...	26m 47s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/node t/pubsub t/router t/script t/secre...	27m 43s
	4h 14m 53s

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