DEB_VERSION is used to set `pkgversion` in the
`override_dh_auto_build` build step. When we moved to the
consolidated source package and thus could no longer use the
default debhelper build tools we lost the automatic setting of
DEB_VERSION, so this change adds the relevant definitions.
Fixes#7724.
Debian reproducibility testing runs a slightly different package
build that seemingly doesn't set the `DEB_BUILD_MULTIARCH` variable.
This change introduces our own environment variable to detect
package builds so that we can skip the ibus-keyman integration
tests that require running an X server.
On local builds we shouldn't upload errors to Sentry. The
`build-utils.sh` script sets the `UPLOAD_SENTRY` environment variable
for that purpose. Also, Sentry doesn't like having an empty string
as pkgversion (which should no longer happen with the rest of this
change, but...)
