Fix misleading summary in docs for FcStrStrIgnoreCase

Reported by Jonathan Kew

Fixes fontconfig/fontconfig#146
2 jobs for issue/146 in 8 minutes and 1 second (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #174232
shared-build

00:08:01

passed #174233
static-build

00:07:20