Virtual job

[SS1823]

virtual job could be used for aggregating other job results.
It would not require a VM

Sample use case is to have "Integration tests" in branch protection rule, and be able to add jobs,
without repo admin permissions.

on: push
jobs:
  test1:
    runs-on: ubuntu-latest
    #...
  test2:
    runs-on: windows-latest
    #...
  all:
    name: Integration tests
    runs-on: virtual
    needs: [test1, test2]

then one could easily add

on: push
jobs:
  test3:
    runs-on: other-machine
    #...
  all:
    name: Integration tests
    runs-on: virtual
    needs: [test1, test2, test3]