Fix OpenGL directional shadow last split fading #13457

Job	Run time
📊 Static checks / Code style, file formatting, and docs	44s
🍏 iOS / Template (target=template_release)	11m 44s
🤖 Android / Template (target=template_release)	22m 32s
🌐 Web / Template (target=template_release)	11m 52s
🐧 Linux / Editor w/ Mono (target=editor)	29m 11s
🍎 macOS / Editor (target=editor, tests=yes)	22m 32s
🐧 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)	32m 51s
🍎 macOS / Template (target=template_release)	6m 3s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	25m 20s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	24m 46s
🏁 Windows / Editor (target=editor, tests=yes)	46m 58s
🐧 Linux / Template w/ Mono (target=template_release)	17m 23s
🏁 Windows / Template (target=template_release)	25m 8s
🐧 Linux / Minimal template (target=template_release, everything disabled)	8m 12s
🪲 Godot CPP / Build and test Godot CPP	9m 41s
	4h 54m 57s

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