Add GitHub Actions job for testing Docker image

[juhoinkinen]

The Docker image is good to be tested before pushing to Quay.io repository.

This PR also reorders the jobs in the GH Actions workflow, so that "publish latest Docker image" is run before "publish release".

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (31ef59d) 99.67% compared to head (1145a4b) 99.67%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #712 +/- ## ======================================= Coverage 99.67% 99.67% ======================================= Files 89 89 Lines 6380 6380 ======================================= Hits 6359 6359 Misses 21 21 ```

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[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

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