Remove clang-18 from compilers CI #674

Job	Run time
omnibus compilations, trigger	4s
omnibus compilations, #2	33m 27s
omnibus compilations, #1	28m 39s
omnibus compilations, #3	25m 52s
omnibus compilations, #5	28m 2s
omnibus compilations, #8	27m 56s
omnibus compilations, #7	34m 2s
omnibus compilations, #10	29m 39s
omnibus compilations, #11	24m 52s
omnibus compilations, #9	27m 43s
omnibus compilations, #12	12m 34s
omnibus compilations, #6	31m 41s
omnibus compilations, #4	25m 52s
omnibus compilations, result	6s
	5h 30m 29s

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