Our file(1) does not have a -v flag.
Lie and produce the version number diffoscope is looking for.

Index: tests/utils/tools.py
--- tests/utils/tools.py.orig
+++ tests/utils/tools.py
@@ -31,7 +31,7 @@ from ..utils.versions import Version
 
 def file_version():
     return (
-        subprocess.check_output(("file", "-v"))
+        subprocess.check_output(("echo", "5.33"))
         .decode("utf-8")
         .splitlines()[0]
         .split("-")[-1]