debian/changelog: Update version

pristine-lfs-source already had policykit-1_0.105-31+apertis2.dsc

Since the filenames does not include the epoch, the below error is seen when the version is updated to 1:0.105-31+apertis2,

$ pristine-lfs -v import-dsc --full --branch "${PRISTINE_SOURCE}" _build-release/*.dsc
I: Importing: _build-release/policykit-1_0.105.orig.tar.gz _build-release/policykit-1_0.105-31+apertis2.debian.tar.xz _build-release/policykit-1_0.105-31+apertis2.dsc
abort: would overwrite files: policykit-1_0.105-31+apertis2.debian.tar.xz, policykit-1_0.105-31+apertis2.dsc

To fix this bump the version to 1:0.105-31+apertis3

Fixes: https://phabricator.apertis.org/T8488