fix: Missing `inline` in `IterativeVertexFinder.ipp` #18465

Job	Run time
cuda	1m 47s
linux_ubuntu	4m 14s
linux_ubuntu_extra (ubuntu2004, 17)	11m 4s
linux_ubuntu_extra (ubuntu2204_cpp20, 20)	5m 27s
linux-nodeps (centos8-lcg100-gcc10)	12m 1s
macos	10m 51s
linux_ubuntu_extra (ubuntu2204_clang, 17)	4m 42s
sycl	2m 34s
linux_examples_test	12m 31s
linux_physmon	25m 40s
linux_physmon_perf_report	0s
	1h 30m 51s

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