[test] Adapt QE test to PE18.08

[lucamar]

Update total energy value: see #375 (comment)

For more information, see the release notes at https://gitlab.com/QEF/q-e/tags/qe-6.2.0

- Some constants in the definition of PBE functionals were truncated to
    6 significant digits. While not a bug, this could lead to tiny differences
    with respect to previous results and other XC implementations (r13592)

Fixes #375.

[vkarak]

lgtm. Thanks @lucamar.

[vkarak]

@jenkins-cscs retry dom

[codecov-io]

Codecov Report

Merging #501 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #501      +/-   ##
==========================================
- Coverage   91.41%   91.39%   -0.03%     
==========================================
  Files          72       72              
  Lines        8737     8737              
==========================================
- Hits         7987     7985       -2     
- Misses        750      752       +2

Impacted Files	Coverage Δ
reframe/core/config.py	82.6% <0%> (-1.74%)	⬇️

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