Maintenance/Maroon-475 Rework CI/CD Pipeline

[mfbrantner]

The new workflow runs all test and build jobs in parallel, taking about 30-40 minutes.

Currently, deployment to Steam only happens when a new commit is pushed to the develop branch, otherwise deployment is skipped.

Since all jobs are executed on infra owned by GitHub, the dedicated runner should no longer be required.

Closes #475. Closes #454.