tests: ignore a warning from h5py that doesn't concern us.

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

pytest.ini

 [pytest]
 junit_family=xunit2
+filterwarnings =
 # this comes from binwalk
 # https://github.com/ReFirmLabs/binwalk/issues/507
-filterwarnings =
     ignore:the imp module is deprecated in favour of importlib.*:DeprecationWarning
+# this comes from h5py
+# https://bugs.debian.org/994617
+    ignore:h5py is running against HDF5 [\d\.]+ when it was built against [\d\.]+, this may cause problems