MoreMesecons/moremesecons_entity_detector/init.lua:68: bad argument #2 to 'set_string' (string expected, got table)

[Bastrabun]

Repro:

Have mesecons, digilines, moremesecons

1. Place mesecons_luacontroller:luacontroller
2. Place moremesecons_entity_detector:entity_detector
3. Add channel "kaputt" to entity_detector
4. Add code to luacontroller: digiline_send("kaputt",{})
5. Press Execute

Crash

AsyncErr: Lua: Runtime error from mod 'mesecons' in callback environment_Step(): .../mods/moremesecons/moremesecons_entity_detector/init.lua:68: bad argument #2 to 'set_string' (string expected, got table)
stack traceback:
	[C]: in function 'set_string'
	.../mods/moremesecons/moremesecons_entity_detector/init.lua:68: in function 'action'
	.../5.10.0/minetest-temp/bin/../mods/digilines/internal.lua:106: in function 'transmit'
	...test/5.10.0/minetest-temp/bin/../mods/digilines/init.lua:60: in function 'receptor_send'
	...emp/bin/../mods/mesecons/mesecons_luacontroller/init.lua:752: in function <...emp/bin/../mods/mesecons/mesecons_luacontroller/init.lua:746>
	...etest-temp/bin/../mods/mesecons/mesecons/actionqueue.lua:131: in function 'execute'
	...etest-temp/bin/../mods/mesecons/mesecons/actionqueue.lua:121: in function <...etest-temp/bin/../mods/mesecons/mesecons/actionqueue.lua:76>
	.../5.10.0/minetest-temp/bin/../builtin/common/register.lua:26: in function <.../5.10.0/minetest-temp/bin/../builtin/common/register.lua:12>

This doesn't happen in 5.8.0, only in 5.9.1 and 5.10.0 and 5.11.0-dev

The difference is in handling of incorrect arguments in case of meta:set_string("key", {}) - it silently unsets the key on 5.8 and errors on 5.9+

Please add a type check

Similar minetest-mods/mesecons#691

For my reference 7743