fix: install libstdcpp for clearlinux

[sevbch]

Context

CI is failing on clearlinux tests because libstdcpp is not installed in the docker image for clearlinux. This is most likely new and coming from the latest version of the docker image but we can't know for sure as the image isn't versioned.

What has been done

• install libstdcpp lib for clearlinux
• cosmetic changes: move all git installs in the new requirements step

Validation

CI failed before, succeeds after.

PR check list

• As much as possible, the changes include tests (unit and/or functional)
• If the changes affect the end user (new feature, behavior change, bug fix) then the PR has a changelog entry (see doc/dev/getting-started.md). If the changes do not affect the end user, then the skip-changelog label has been added to the PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.91%. Comparing base (f78efe7) to head (1f87a61).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1106   +/-   ##
=======================================
  Coverage   91.91%   91.91%           
=======================================
  Files         144      144           
  Lines        6094     6094           
=======================================
  Hits         5601     5601           
  Misses        493      493           

Flag	Coverage Δ
unittests	91.91% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[agateau-gg]

Approved with a request for comment :)