docs: correct C return annotation in `stats/base/dists/geometric/stdev` #25225

Job	Run time
Check for stale label	0s
Check for contributor guidelines label	0s
Check for project conventions label	0s
Check for Git History label	0s
Check for already resolved label	0s
Check for spam label	0s
Check for EditorConfig label	0s
	0s

Provide feedback