iwyu.yml: added `diskarzhan` job #521

Job	Run time
clang-include-cleaner (libstdc++)	8m 31s
clang-include-cleaner (libc++)	10m 22s
iwyu (ubuntu-22.04, fedora:rawhide, libc++)	7m 50s
diskarzhan	13s
iwyu (ubuntu-22.04, fedora:rawhide, libstdc++)	6m 37s
iwyu (macos-26, libc++, -Xiwyu --mapping_file=$(realpath ./macos.imp))	5m 41s
	39m 14s

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