Support multiple asserts of same type

[evilrobot-01]

Currently one cannot have multiple asserts of the same type, as keys need to be unique. As an example:

              - asserts:
                  equal:
                    args: [ true, true ]
                  equal:
                    args: [ true, true ]

This results in YAMLSemanticError: Map keys must be unique; "equal" is repeated.

Switching to using dashed notation works around this:

              - asserts:
                  - equal:
                      args: [ true, true ]
                  - equal:
                      args: [ true, true ]

But this then results in an issue when resolving the asserts, where the key name is its index (0,1 etc.) rather than the assert name (equal):

A workaround is to separate them into additional assert sections, but having a single assert section would be ideal:

              - asserts:
                  equal:
                    args: [ true, true ]
              - asserts:
                  equal:
                    args: [ true, true ]