tests: add switch to move executions between google and openstack

[sergiocazzolato]

Through this change it is possible to determine if the alternative backend has to be used for the a group in the ci
Alternative backends usage depends on the value stored in the file USE_ALTERNATIVE_BACKEND, where it is defined the backend to use when images are ready in both google and openstack.

The content for USE_ALTERNATIVE_BACKEND is:
opensuse: false,
debian-not-req: false,
centos: false,
ubuntu-jammy: false,
ubuntu-focal (fundamental): false,
ubuntu-noble (fundamental): false

In case we need to swith a group, we just need to change false by true

[maykathm]

I think you're missing the piece that passes the alternative-backend entry to the spread-tests.yaml workflow. I believe it should be something like:

    uses: ./.github/workflows/spread-tests.yaml
    with:
      runs-on: '["self-hosted", "spread-enabled"]'
      group: ${{ matrix.group }}
      backend: ${{ matrix.backend }}
      alternative-backend: ${{ matrix.alternative-backend }}
      systems: ${{ matrix.systems }}
      tasks: ${{ matrix.tasks }}
      rules: ${{ matrix.rules }}

Unfortunately, that will mean that alternative-backend entry has to be present in every other group in the jsons, otherwise the test.yaml will break.

[github-actions]

Wed Feb 26 16:23:45 UTC 2025
The following results are from: https://github.com/canonical/snapd/actions/runs/13546745136

Failures:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.07%. Comparing base (a272aac) to head (67940b8).
Report is 59 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #15122    +/-   ##
========================================
  Coverage   78.07%   78.07%            
========================================
  Files        1182     1183     +1     
  Lines      157743   158157   +414     
========================================
+ Hits       123154   123480   +326     
- Misses      26943    27005    +62     
- Partials     7646     7672    +26     

Flag	Coverage Δ
unittests	78.07% <ø> (+<0.01%)	⬆️

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