tests/usb: Skip the removal tests when the UMockdev version is too old

We disabled the test in CI because the tests were failing but we didn't
understand why in

06a5e50 ("test: Disable USB removal test in a container")

It turns out that UMockdev simply didn't send the remove event before
version 0.18.4. Let's change the skip condition to actually check for
the right thing instead of just disabling it in CI. This means that the
test will run in CI once ubuntu:latest does have the right version.

tests/test_usb.py

@@ -7,6 +7,7 @@
 import pytest
 import os
 import gi
+import subprocess
 
 gi.require_version("UMockdev", "1.0")
 from gi.repository import GLib, UMockdev  # noqa E402
@@ -22,6 +23,16 @@ def umockdev():
     return UMockdev.Testbed.new()
 
 
+def umockdev_has_working_remove():
+    # umockdev only generates remove events since version 0.18.4
+    # https://github.com/martinpitt/umockdev/releases/tag/0.18.4
+    required = (0, 18, 4)
+
+    result = subprocess.run(["umockdev-run", "--version"], stdout=subprocess.PIPE)
+    version = tuple(map(int, result.stdout.decode("UTF-8").strip().split(".")))
+    return all(v >= r for v, r in zip(version, required))
+
+
 class TestUsb:
     _num_devices = 0
 
@@ -188,7 +199,9 @@ def cb_device_events(session_handle, events):
             )
 
     @pytest.mark.parametrize("usb_queries", ["vnd:04a9", None])
-    @pytest.mark.skipif(xdp.is_in_container(), reason="Test fail in containers")
+    @pytest.mark.skipif(
+        not umockdev_has_working_remove(), reason="UMockdev version 0.18.4 required"
+    )
     def test_device_remove(self, portals, dbus_con, app_id, usb_queries, umockdev):
         usb_intf = xdp.get_portal_iface(dbus_con, "Usb")