CI process mysteriously fails

[MarcoGorelli]

See here

=================================== FAILURES ===================================
______________ TestMarginalKron.testMarginalKronvsMarginalpredict ______________
[gw1] linux -- Python 3.6.11 /usr/share/miniconda/envs/testenv/bin/python

self = <pymc3.tests.test_gp.TestMarginalKron object at 0x7f5cf6c46240>

    def testMarginalKronvsMarginalpredict(self):
        with pm.Model() as kron_model:
            kron_gp = pm.gp.MarginalKron(mean_func=self.mean, cov_funcs=self.cov_funcs)
            f = kron_gp.marginal_likelihood("f", self.Xs, self.y, sigma=self.sigma, shape=self.N)
            p = kron_gp.conditional("p", self.Xnew)
            mu, cov = kron_gp.predict(self.Xnew)
        npt.assert_allclose(mu, self.mu, atol=0, rtol=1e-2)
Unable to revert mtime: /usr/share/fonts
>       npt.assert_allclose(cov, self.cov, atol=0, rtol=1e-2)
Unable to revert mtime: /usr/share/fonts/cMap
E       AssertionError: 
Unable to revert mtime: /usr/share/fonts/cmap
E       Not equal to tolerance rtol=0.01, atol=0
Unable to revert mtime: /usr/share/fonts/truetype
Unable to revert mtime: /usr/share/fonts/type1
Unable to revert mtime: /usr/share/fonts/cmap/adobe-cns1
Unable to revert mtime: /usr/share/fonts/cmap/adobe-gb1
Unable to revert mtime: /usr/share/fonts/cmap/adobe-japan1
Unable to revert mtime: /usr/share/fonts/cmap/adobe-japan2
Unable to revert mtime: /usr/share/fonts/cmap/adobe-korea1
Unable to revert mtime: /usr/share/fonts/truetype/dejavu
Unable to revert mtime: /usr/share/fonts/truetype/droid
Unable to revert mtime: /usr/share/fonts/truetype/lato
Unable to revert mtime: /usr/share/fonts/truetype/liberation
Unable to revert mtime: /usr/share/fonts/truetype/noto
Unable to revert mtime: /usr/share/fonts/type1/gsfonts
E       
E       Mismatched elements: 2 / 25 (8%)
E       Max absolute difference: 1.04653081e-06
E       Max relative difference: 0.04904542
E        x: array([[ 9.779797e-01,  3.392796e-22,  3.950869e-06, -2.558771e-12,
E                1.137622e-06],
E              [ 3.392796e-22,  1.000000e+00,  4.022414e-21,  7.814298e-33,...
E        y: array([[ 9.779807e-01,  3.393030e-22,  3.950869e-06, -2.558771e-12,
E                1.137622e-06],
E              [ 3.393030e-22,  1.000001e+00,  4.022414e-21,  7.448961e-33,...

pymc3/tests/test_gp.py:1147: AssertionError

---

This test passes when run locally, and it also passed when the PR was opened. Can't figure out what these (seemingly spurious?) Unable to revert mtime errors are

[MarcoGorelli]

Looking around, it seems that the Unable to revert mtime messages can be ignored

If the absolute difference here is just of 1e-6, maybe the test can simply be made a little less strict