Specify deps in docs extra instead

.readthedocs.yaml

@@ -9,6 +9,13 @@ formats:
   - epub
   - htmlzip
 
+python:
+  install:
+    - method: pip
+      path: .
+      extra_requirements:
+        - docs
+
 build:
   os: ubuntu-22.04
   apt_packages:
@@ -25,10 +32,3 @@ build:
       - cd docs/build/ && latexmk -r latexmkrc -pdf -f -dvi- -ps- -jobname=pybamm-eis -interaction=nonstopmode || true
       - test -f docs/build/pybamm-eis.pdf && echo "pybamm-eis.pdf exists. Copying source file to $READTHEDOCS_OUTPUT/pdf/."
       - cp "docs/build/pybamm-eis.pdf" $READTHEDOCS_OUTPUT/pdf/
-
-python:
-  install:
-    - method: pip
-      path: .
-      extra_requirements:
-        - myst-parser

pyproject.toml

@@ -17,3 +17,12 @@ packages = [
 [tool.setuptools.dynamic]
 version = {attr = "pbeis.version.__version__"}
 readme = {file = ["README.md"], content-type = "text/markdown"}
+
+[project.optional-dependencies]
+docs = [
+    # Sphinx extensions
+    "sphinx.ext.autodoc",
+    "sphinx.ext.mathjax",
+    # Third-party extensions
+    "myst_parser",
+    ]