[vim9]Memory Leak when assigning a lambda function decorated in a HigherOrder function to a variable

[Chen-Rong-Zi]

Steps to reproduce

vim9script

def HigherOrder(Function: func): func
    def Inner(): string
        # add decoration
        return Function()
    enddef
    return Inner
enddef

def MemoryLeakTest()
    const must_used_variable = ''"
    var F: func = HigherOrder(() => must_used_variable)
enddef

# for more noticeable memory leak
nnoremap <leader><leader> <ScriptCmd> for i in range(10000) \| MemoryLeakTest() \| endfor<CR>

source the code above, after pressing <leader>key multiple times, i get the this result in btop

To trigger this problem, there are at least three requirements

1. refering to a variable that is in closure scope (must_used_variable in this case)
2. use a higher order function to decorate a lambda function
3. assigning this lambda function to a variable

otherwise, vim works fine and this problem will not be triggered

Expected behaviour

I have a function, which is frequently called, works just like the above one.
vim soon comsumes more memory than I expected.
I expect that functions like this should work with no memory leak problem.

Version of Vim

9.1.380

Environment

OS: 6.1.90-1-MANJARO
terminal: alacritty 0.8.0-dev (3ed0430)
$TERM="xterm-256color"
shell: bash 5.2.26

Logs and stack traces

<SNR>15_HigherOrder
    def Inner(): string
        # add decoration
        return Function()
    enddef
   0 FUNCREF <lambda>75
   1 STORE $0

    return Inner
   2 LOAD $0
   3 RETURN


<SNR>15_MemoryLeakTest
    const must_used_variable = ''
   0 PUSHS ""
   1 LOCKCONST
   2 STORE $0

    var F: func = HigherOrder(() => must_used_variable)
   3 FUNCREF <lambda>74
   4 DCALL <SNR>15_HigherOrder(argc 1)
   5 STORE $1
   6 RETURN void