Fix docker image builds and uploads for new releases

[giffels]

Currently, docker image are build on new tags, but not pushed to docker due to the following buggy constraint.

if github.repository == 'MatterMiners/tardis' && github.ref == 'refs/heads/master'

However, tags are in refs/tags. The constraint was added in order avoid uploading docker images build for each pull request. This pull request achieves the same by using the following contraint instead.

if: github.repository == 'MatterMiners/tardis' && github.event_name != 'pull_request'

In addtion, I have switched building and uploading of docker images for branches other then master. Since we solely work with pull requests so far.

Thanks to @QuantumDancer for reporting that issue.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (36ac7c1) 98.86% compared to head (cbf573e) 98.86%.

:exclamation: Current head cbf573e differs from pull request most recent head 9433826. Consider uploading reports for the commit 9433826 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #316 +/- ## ======================================= Coverage 98.86% 98.86% ======================================= Files 55 55 Lines 2210 2210 ======================================= Hits 2185 2185 Misses 25 25 ```

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