regex.cpp: fixed `unmatchedSuppression` (#8617) #19943

Job	Run time
build_make (ubuntu:25.10)	3m 15s
build_make (ubuntu:24.04)	4m 14s
build_cmake (alpine:3.23, false, false)	4m 23s
build_cmake (ubuntu:25.10, true, true)	3m 14s
build_cmake (ubuntu:24.04, true, true)	4m 58s
build_make (alpine:3.23)	5m 39s
	25m 43s

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