containers: Make webpack-jumpstart --partial in unit test opportunistic

This *will* fail on any PR which changes package.json/rebuilds
node_modules, with "Unable to find any suitable commit". That's fine, we
have to bite the bullet and rebuild the webpack ourselves then. We could
alternatively use `--wait`, but that would not save wallclock time, just
some CPU usage.

Do the same thing as test/run, and ignore failures.

containers/unit-tests/start

@@ -86,7 +86,7 @@ class SourceDirectory(PodmanTemporaryDirectory):
             if args.wait:
                 run([f'{self.name}/tools/webpack-jumpstart', '--wait'], check=True)
             elif not args.no_jumpstart:
-                run([f'{self.name}/tools/webpack-jumpstart', '--partial'], check=True)
+                run([f'{self.name}/tools/webpack-jumpstart', '--partial'], check=False)
 
 
 class ResultsDirectory(PodmanTemporaryDirectory):