ci: investigate why Read the docs doesn't register versions after v1.7.7

[juarezr]

Problem description

What's happenning

A clear and concise description of what the bug is. Please explain:

• Read the docs can store all generated versions of the manual.
• However this stopped after v1.7.7

Expected behavior

A clear and concise description of intended behavior. Please explain:

• When a new release is triggered in the Gihub Actions:
  • Read the docs should update the latest and stable versions.
  • Also Read the docs should have a v1.X.Y entry for versioning.

Scenario for reprodution

Reproducible test case

Please provide a minimal, reproducible code sample, a copy-pastable example if possible:

• Check Read the docs:
  • Click on the v:latest button at the bottom left corner
  • You see that the versioning stops as v1.7.7
  • However latest and stable are working.

Version and installation information

Please provide the following:

• Value of petl.__version__: v1.7.13
• How petl was installed:
  • Docs are built in the CI and registered in Read the docs after.

Also, if you think it might be relevant, please provide the output from pip freeze or
conda env export depending on which was used to install petl.

Additional context

Add any other context about the problem here.

Also, feel free to remove all sections and text that aren't relevant.