Doc: updates to support building with upcoming update proj-docs Docke…

…r image updated to Ubuntu 24.04

I've tested locally those changes with a local build of the updated
proj-docs Docker image per OSGeo/PROJ#4128

.github/workflows/doc_build.yml

@@ -30,7 +30,7 @@ jobs:
           apt update
           apt install -y libproj-dev swig
           python3 -m pip install -r doc/requirements.txt
-          python3 -m pip install numpy
+          python3 -m pip install numpy setuptools
           pushd .
           mkdir build
           cd build
@@ -43,6 +43,14 @@ jobs:
             -DOGR_BUILD_OPTIONAL_DRIVERS=OFF
           cmake --build . -j$(nproc)
           cmake --install .
+          # With the new ghcr.io/osgeo/proj-docs image based on Ubuntu 24.04
+          # a venv is activated. The above does not install the
+          # Python bindings into it (and the ones in the system are not found
+          # without overriding PYTHONPATH), so do it through pip install
+          cd swig/python
+          python3 setup.py sdist
+          cp dist/* /tmp/gdal.tar.gz
+          python3 -m pip install /tmp/gdal.tar.gz
           ldconfig
           popd
 

doc/source/conf.py

@@ -441,14 +441,30 @@
 \fi
 """
 
+# Package substitutefont no longer exists since TeXLive 2023 later than August 2023
+# and has been replaced with sphinxpackagesubstitutefont
+# https://github.com/jfbu/sphinx/commit/04cbd819b0e285d058549b2173af7efadf1cd020
+import sphinx
+
+if os.path.exists(
+    os.path.join(
+        os.path.dirname(sphinx.__file__), "texinputs", "sphinxpackagesubstitutefont.sty"
+    )
+):
+    substitutefont_package = "sphinxpackagesubstitutefont"
+else:
+    substitutefont_package = "substitutefont"
+
 latex_elements = {
     # The paper size ('letterpaper' or 'a4paper').
     #'papersize': 'letterpaper',
     # The font size ('10pt', '11pt' or '12pt').
     #'pointsize': '10pt',
     # Additional stuff for the LaTeX preamble.
     "preamble": preamble,
-    "inputenc": "\\usepackage[utf8]{inputenc}\n\\usepackage{CJKutf8}\n\\usepackage{substitutefont}",
+    "inputenc": "\\usepackage[utf8]{inputenc}\n\\usepackage{CJKutf8}\n\\usepackage{"
+    + substitutefont_package
+    + "}",
     "babel": "\\usepackage[russian,main=english]{babel}\n\\selectlanguage{english}",
     "fontenc": "\\usepackage[LGR,X2,T1]{fontenc}"
     # Latex figure (float) alignment