Do not warn about missing tlsh during tests

See the comments in
#29 for
more background, as well as the thread at
https://lists.reproducible-builds.org/pipermail/diffoscope/2020-June/002642.html



Signed-off-by: Mattia Rizzolo <mattia@debian.org>

diffoscope/main.py

@@ -658,7 +658,7 @@ def run_diffoscope(parsed_args):
 
     ProfileManager().setup(parsed_args)
     PresenterManager().configure(parsed_args)
-    if not tlsh:
+    if not tlsh and "PYTEST_CURRENT_TEST" not in os.environ:
         logger.warning(
             'Fuzzy-matching is currently disabled as the "tlsh" module is unavailable.'
         )