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: https://github.com/tholo/pytest-flake8/issues/87

[codecov[bot]]

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

```diff @@ 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%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HEPCloud#carryforward-flags-in-the-pull-request-comment) to find out more.

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