Redundant tag-push check in push step of container image build workflow file

The workflow is configured to trigger on a push of a git tag: https://github.com/DiamondLightSource/TomoHub/blob/c931d678180cb6c53a55f214e9672e38b6300775/.github/workflows/_tomohub.yml#L3-L6

and yet the final step is checking if the event was a "push" and if there's a tag before the step runs (which is pushing the built container image): https://github.com/DiamondLightSource/TomoHub/blob/c931d678180cb6c53a55f214e9672e38b6300775/.github/workflows/_tomohub.yml#L59

The latter check is redundant due to the former already constraining the workflow to run only on a push of a tag.

Inspect .github/workflows/_tomohub.yml, especially the tag trigger near lines 3-6 and the final container-image push step near line 59. Confirm the trigger already limits runs to tag pushes, then remove the redundant condition and verify the workflow still pushes the image for tag-triggered runs.

Written by the indexing model from the issue text.