Fix memory leak in test args

[Xrayez]

With the #40928, this allows #40920 to pass the tests with sanitizer.

==24982==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 47 byte(s) in 2 object(s) allocated from:
    #0 0x7fa785b20618 in operator new[](unsigned long) (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xe0618)
    #1 0x1bac644 in test_main(int, char**) tests/test_main.cpp:76
    #2 0x1a55116 in Main::test_entrypoint(int, char**, bool&) main/main.cpp:380
    #3 0x1973940 in main platform/linuxbsd/godot_linuxbsd.cpp:45
    #4 0x7fa782ad1b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)

SUMMARY: AddressSanitizer: 47 byte(s) leaked in 2 allocation(s).

P.S. My first bug fix with sanitizer's help. 😛

[akien-mga]

Thanks!