gnu: python-fenics-dijitso: Fix tests.

* gnu/packages/simulation.scm (python-fenics-dijitso)
[native-inputs]: Re-introduce python-pytest-cov.

Change-Id: I8ade39f8dbac62eea8f978c70d88310a00ad7581
Signed-off-by: Sharlatan Hellseher <sharlatanus@gmail.com>

gnu/packages/simulation.scm

@@ -795,8 +795,9 @@ some support for generating and analysing traffic scenarios..")
                   (invoke "./runtests.sh"))))))))
     (native-inputs
      (list python-pytest
-           python-setuptools
-           python-wheel))
+           ;; This package has a custom way to run tests.
+           python-pytest-cov
+           python-setuptools))
     (inputs
      (list openmpi python-numpy))
     (propagated-inputs