BLD: Add myst_parser to CI

Adds this to env-template.yml for inclusion into images, and temporarily also adds it
to .gitlab-ci.yml for more immediate testing purposes.

.gitlab-ci.yml

@@ -230,6 +230,7 @@ docs:
   script:
     # Make the documentation
     - python -m pip install .
+    - python -m pip install myst_parser # only for testing purposes - remove once test image is generating correctly
     - cd examples/tutorials
     - jupyter nbconvert --to notebook --execute *.ipynb --output-dir ../../docs
     - cd ../../docs

containers/env-template.yml

@@ -69,6 +69,7 @@ dependencies:
   - nbconvert
   - twine
   - glasflow
+  - myst_parser
   - pip:
     - autodoc
     - ipykernel