Run SBT clean before CI build

[4e6]

Pull Request Description

Changelog:

• update: run clean SBT command before running other commands on CI

Important Notes

This is a low-effort attempt to stabilize the backend building on CI. The problem is that each time the branch is picked up by a random worker that has an arbitrary state of the SBT cache. And because SBT can not track dependencies perfectly in our project due to the heavy annotations and preprocessor usage, it results in sporadic build failures.

Other approaches:

• @JaroslavTulach suggested to attach Clean build required label using the Labeler action each time the engine sources are modified. But it will require significantly more work to integrate this extra step because it needs to be executed before other build steps.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.

[JaroslavTulach]

Shouldn't the clean only run for those who modify engine sources? It should be possible to detect what files are changed in the PR: https://stackoverflow.com/questions/74265821/get-modified-files-in-github-actions

[4e6]

It does not matter if the current branch modified engine sources or not. It can be the case that the runner that picked up the job previously was building the branch that did and has an SBT cache left from building that branch.