Remove clang-18 from compilers CI #724

Job	Run time
Windows 2022/Visual C++ 2022 (check)	24m 26s
Windows 2025/Visual C++ 2022 (check)	26m 16s
Windows 2025/Visual C++ 2022 (test-bundled-gems)	25m 36s
Windows 11-arm/Visual C++ (btest test-basic test-tool)	15m 40s
Windows result	2s
	1h 32m 0s

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