Prevent read-after-free in the queued CallableCustomStaticMethodPointer, fixes `slot >= slot_max` errors in release templates #16265

Job	Run time
📊 Static checks / Code style, file formatting, and docs	35s
🍏 iOS / Template (target=template_release)	11m 28s
🍎 macOS / Editor (target=editor, tests=yes)	35m 55s
🍎 macOS / Template (target=template_release)	29m 7s
🤖 Android / Template (target=template_release)	24m 32s
🌐 Web / Template (target=template_release)	14m 34s
🐧 Linux / Editor w/ Mono (target=editor)	28m 15s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)	25m 27s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	26m 6s
🏁 Windows / Editor (target=editor, tests=yes)	34m 50s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	24m 5s
🏁 Windows / Template (target=template_release)	23m 37s
🐧 Linux / Template w/ Mono (target=template_release)	17m 48s
🐧 Linux / Minimal template (target=template_release, everything disabled)	12m 37s
🪲 Godot CPP / Build and test Godot CPP	6m 49s
	5h 15m 45s

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