smoketest: 30 runs a baseline's install once more if it fails

voxtype's build from source fails now and then at link time, with
Vulkan shaders missing: 0c0ddf5 built it in two runs and not the third,
with the same packages. The baseline isn't what's under test, and the
old installers skip what they already installed, so try once more.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

smoketest/scenarios/30-upgrade-from-baseline.sh

@@ -42,6 +42,13 @@ scenario() {
   assert_status 0
 
   cd_install
+  # voxtype's build from source fails now and then (Vulkan shaders missing at
+  # link time), and the baseline isn't what's under test: try once more, as
+  # someone would. The installer skips what it already installed
+  if [ "$STATUS" -ne 0 ]; then
+    echo "The baseline's install failed; running it once more"
+    cd_install
+  fi
   assert_status 0
   run_in_vm reset "sudo rm /etc/polkit-1/rules.d/00-smoketest-flatpak.rules
     git -C ~/.local/share/coredesktop reset -q --hard $(q "$sha")"