Add conflict in fork scenario

[konstin]

Add a scenario where we fail after forking. The error message is already not bad:

  × No solution found when resolving dependencies:
  ╰─▶ Because only fork-basic-b-03509d5c==1.0.0 is available and fork-basic-b-03509d5c==1.0.0 depends on fork-basic-d-03509d5c==1,
      we can conclude that all versions of fork-basic-b-03509d5c depend on fork-basic-d-03509d5c==1.
      And because fork-basic-c-03509d5c==1.0.0 depends on fork-basic-d-03509d5c==2 and only fork-basic-c-03509d5c==1.0.0 is
      available, we can conclude that all versions of fork-basic-b-03509d5c and all versions of fork-basic-c-03509d5c are
      incompatible.
      And because fork-basic-a-03509d5c{sys_platform == 'darwin'}==1.0.0 depends on fork-basic-b-03509d5c and fork-basic-c-03509d5c,
      we can conclude that fork-basic-a-03509d5c{sys_platform == 'darwin'}==1.0.0 cannot be used.
      And because only the following versions of fork-basic-a-03509d5c{sys_platform == 'darwin'} are available:
          fork-basic-a-03509d5c{sys_platform == 'darwin'}==1.0.0
          fork-basic-a-03509d5c{sys_platform == 'darwin'}>=2
      and fork-basic-03509d5c==0.0.0 depends on fork-basic-a-03509d5c{sys_platform == 'darwin'}<2, we can conclude that
      fork-basic-03509d5c==0.0.0 cannot be used.
      And because only fork-basic-03509d5c==0.0.0 is available and you require fork-basic-03509d5c, we can conclude that the
      requirements are unsatisfiable.