[ci] Add missing dependency and fix RTD config

Cairo libraries are required for a python dependency.
New RTD config introduced to fix build errors introduced by new urllib.
We need to ensure the docs a built on a modern ubuntu with a
sufficiently new python (see
https://github.com/readthedocs/readthedocs.org/issues/10290).

.readthedocs.yml

@@ -0,0 +1,20 @@
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Set the version of Python and other tools you might need
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.11"
+
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+   configuration: doc/conf.py
+
+python:
+   install:
+   - requirements: doc/requirements.txt

ci/install-build-deps.sh

@@ -49,7 +49,8 @@ case "$ID-$VERSION_ID" in
         libelf-dev \
         clang-format \
         wget \
-        xz-utils
+        xz-utils \
+        libcairo2-dev
 
     wget https://storage.googleapis.com/ibex-cosim-builds/ibex-cosim-"$IBEX_COSIM_VERSION".tar.gz
     $SUDO_CMD mkdir -p /tools/riscv-isa-sim