Tests: Fix ExternalProject CONFIGURE_HANDLED_BY_BUILD on 1s filesystems

Following commit 7155e358 (ExternalProject: Add CONFIGURE_HANDLED_BY_BUILD
option, 2020-12-16, v3.20.0-rc1~168^2), modify the CONFIGURE_HANDLED_BY_BUILD
test to sleep 1.125 seconds to make sure the file timestamp is always
updated regardless of the resolution of the underlying filesystem.

Fixes: #21830