CI: Only build packages on install in bump_autobuild job

This will still build outdated packages in the bump_autobuild packages,
which isn't good—but I don't know any way of avoiding that.

Closes https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/issues/2625

.ci/integration.sh

@@ -29,6 +29,9 @@ pmbootstrap -q shutdown
 # Default for tests where the device doesn't matter
 pmbootstrap config device qemu-amd64
 
+# Building packages takes long, only do it if actually relevant to the test.
+pmbootstrap config build_pkgs_on_install False
+
 # A test that builds normal and FDE images for the given device/ui
 build_images() {
 	device="$1"
@@ -95,6 +98,7 @@ bump_autobuild() {
 	fi
 
 	pmbootstrap config device "$device"
+	pmbootstrap config build_pkgs_on_install True
 
 	echo "Bumping pkgrel of $package"
 	# shellcheck disable=SC2086