.gitlab-ci.yml: allow rawhide builds to fail

[junghans]

Part of votca/votca#159

Workaround for openucx/ucx#3558

[codecov]

Codecov Report

Merging #145 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #145   +/-   ##
======================================
  Coverage    63.9%   63.9%           
======================================
  Files          92      92           
  Lines        4945    4945           
======================================
  Hits         3161    3161           
  Misses       1784    1784

Flag	Coverage Δ
#clang	69.4% <ø> (ø)	⬆️
#doxygen	32.5% <ø> (ø)	⬆️
#gcc	69.9% <ø> (ø)	⬆️

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