Enable some tests only on DE 1.7 branch

[vitodb]

Enable tests that run on EL7 only for DE branch 1.7, those are
rpmbuild_el7 in ci.yaml
pytest_el7 in pytest.yaml

Also enable run_flake8 only on DE branch 1.7 as this relays on pytest-flake8 module that doesn't work with flake8 >= 5.0:
tholo/pytest-flake8#87

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (97915e0) 97.25% compared to head (c91a368) 97.25%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #685   +/-   ##
=======================================
  Coverage   97.25%   97.25%           
=======================================
  Files          51       51           
  Lines        3165     3165           
  Branches      517      517           
=======================================
  Hits         3078     3078           
  Misses         54       54           
  Partials       33       33           

Flag	Coverage Δ
python-3.11	97.21% <ø> (ø)
python-3.9	97.21% <ø> (+0.03%)	⬆️

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