test: support slow test-ukify on Debian/Ubuntu

Kernels are installed in /boot/ so find them there too

src/ukify/test/test_ukify.py

@@ -411,6 +411,8 @@ def test_help_error(capsys):
 @pytest.fixture(scope='session')
 def kernel_initrd():
     items = sorted(glob.glob('/lib/modules/*/vmlinuz'))
+    if not items:
+        items = sorted(glob.glob('/boot/vmlinuz*'))
     if not items:
         return None