Work around tox not following its docs

`--parallel-no-spinner` is supposed to imply `--parallel`, but apparently,
that's not working for us.

Author: robsdedude

testkit/unittests.py

@@ -18,4 +18,14 @@
 
 
 if __name__ == "__main__":
-    run_python(["-m", "tox", "-vv", "--parallel-no-spinner", "-f", "unit"])
+    run_python(
+        [
+            "-m",
+            "tox",
+            "-vv",
+            "--parallel",
+            "--parallel-no-spinner",
+            "-f",
+            "unit",
+        ]
+    )