Workflow slow-checks.yml: ask for manual approval in separate job

[ckunki]

Currently, PTB workflow template slow-checks.yml contains 2 jobs: build-matrix and Tests.

Only job Tests uses environment manual-approval.
If the user does not manually approve running job Tests then still job build-matrix is executed, but remains unused.

AC

• Both jobs use same naming convention, e.g. capitalized with Dashes.
• PTB workflow template slow-checks.yml contains a separate job named "Run Slow Checks"
• Both jobs build-matrix and Tests link to the new job with needs
• You can achieve the same result by adding a job into file merge-gate.yml before calling ./.github/workflows/slow-checks.yml
• In file merge-gate.yml ./.github/workflows/slow-checks.yml is called with secrets: inherit
  • Background: slow checks often involve additional resources, e.g. SaaS databases or cloud resources
  • Accessing these resources requires additional secrets (e.g. credentials or tokens)
  • These secrets need to be inherited