Fix building docs in CI

Older versions of Sphinx don't work with whatever the default version of
Python is on GitHub Actions, and never versions of Sphinx need a newer
version of Python.

Also update the RTD theme and Breathe while I'm at it.

.github/workflows/ci.yml

@@ -123,6 +123,10 @@ jobs:
           ./libloot_internals_tests
           ./libloot_tests
 
+      - uses: actions/setup-python@v2
+        with:
+          python-version: '3.10'
+
       - name: Install packages for building docs
         shell: bash
         run: |
@@ -201,6 +205,10 @@ jobs:
           .\libloot_internals_tests.exe
           .\libloot_tests.exe
 
+      - uses: actions/setup-python@v2
+        with:
+          python-version: '3.10'
+
       - name: Install packages for building docs
         run: |
           nuget install doxygen -Version 1.8.14

.github/workflows/release.yml

@@ -99,6 +99,10 @@ jobs:
           ./libloot_internals_tests
           ./libloot_tests
 
+      - uses: actions/setup-python@v2
+        with:
+          python-version: '3.10'
+
       - name: Install packages for building docs
         shell: bash
         run: |
@@ -174,6 +178,10 @@ jobs:
           cmake .. -G "Visual Studio 15 2017" -A ${{ matrix.platform }} -DBOOST_ROOT="boost_1_72_0" -DCPACK_PACKAGE_VERSION="${{ steps.get-libloot-version.outputs.version }}"
           cmake --build . --config ${{ env.MSVC_CONFIG }}
 
+      - uses: actions/setup-python@v2
+        with:
+          python-version: '3.10'
+
       - name: Install packages for building docs
         run: |
           nuget install doxygen -Version 1.8.14

.readthedocs.yml

@@ -6,6 +6,6 @@ sphinx:
 formats: all
 
 python:
-  version: 3.7
+  version: 3.10
   install:
     - requirements: docs/requirements.txt

docs/requirements.txt

@@ -1,3 +1,3 @@
-sphinx==2.0.1
-sphinx_rtd_theme==0.4.3
-breathe==4.13.0
+sphinx==4.2.0
+sphinx_rtd_theme==1.0.0
+breathe==4.31.0