WIP: [ci] [R-package] re-enable clang-18 testing (fixes #6369) #8575

Job	Run time
r-package (ubuntu-latest, gcc, R 3.6, cmake)	8m 31s
r-package (ubuntu-latest, gcc, R 4.3, cmake)	9m 57s
r-package (ubuntu-latest, clang, R 3.6, cmake)	8m 34s
r-package (ubuntu-latest, clang, R 4.3, cmake)	10m 16s
r-sanitizers (ubuntu-latest, R-devel, gcc ASAN/UBSAN)	15m 15s
r-sanitizers (ubuntu-latest, R-devel, clang ASAN/UBSAN)	28m 56s
r-package (macos-13, gcc, R 4.3, cmake)	10m 48s
r-package (macos-13, clang, R 4.3, cmake)	10m 27s
r-package (windows-latest, MINGW, R 3.6, cmake)	12m 30s
r-package (windows-latest, MINGW, R 4.3, cmake)	16m 47s
r-package (windows-2019, MSVC, R 3.6, cmake)	25m 8s
r-package (windows-2022, MSVC, R 4.3, cmake)	30m 8s
r-package (windows-latest, MINGW, R 3.6, cran)	19m 28s
r-package (windows-latest, MINGW, R 4.3, cran)	18m 7s
r-package (ubuntu-latest, gcc, R 4.3, cran)	15m 50s
r-package (macos-13, clang, R 4.3, cran)	18m 26s
r-package (debian, R-devel, clang-16)	8m 48s
r-package (debian, R-devel, clang-17)	8m 33s
r-package (ubuntu, R-devel, clang-18)	4m 34s
all-r-package-jobs-successful	2s
	4h 41m 5s

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