Sergey,

This patch moves the aforementioned test from the <misc> to the <lang/>
directory (with slightly renaming to be consistent with other names),
includes it in <index>, and names the subtest.

Also, it changes the number of iterations to trigger the GC since the
number of objects is different when running the test as a part of the
LuaJIT test suite.

Part of tarantool/tarantool#9398
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