Add LLVM 18 to LLVM CI #11294

Job	Run time
check_format	1m 51s
deploy_api_docs	0s
x86_64-gnu-test (1.7.3)	34m 26s
x86_64-gnu-test (1.8.2)	33m 35s
x86_64-gnu-test-preview_mt	5m 51s
x86_64-musl-test	39m 14s
x86_64-gnu-test (1.9.2)	32m 27s
x86_64-gnu-test (1.10.1)	32m 42s
x86_64-gnu-test (1.11.2)	31m 39s
x86_64-gnu-test (1.12.1)	31m 34s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	31m 36s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	35m 7s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	32m 59s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	33m 30s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	33m 9s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	34m 1s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	33m 30s
	7h 57m 11s

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