Problem resolving explicit nodes

[scarlehoff]

There's a few problems when resolving the explicit node of the covmat.

Some of these which involved the theory covmat have already been identified and will be solved in #1910 but some remain:

meta:
    title: Example of bug
    keywords: [example]

pdfs:
    - id: NNPDF40_nnlo_lowprecision

theoryid: 162

use_cuts: "internal"

dataset_inputs:
      - { dataset: BCDMSP}

template_text: |
  {@ dataset_inputs::pdfs plot_fancy(normalize_to=data)@}

actions_:
  - report(main=true)

(the strange thing is that if I add {@ dataset_inputs plot_fancy @} in the template_text, the runcard works.

I don't know since when this bug has been around, but it is not new. I can reproduce it also with code from 2020 (nnpdf tag 4.0.0 and reportengine 0.29).

[scarlehoff]

This is actually the same as #1493