Update doc image

Author: vitaut

.github/workflows/doc.yml

@@ -7,8 +7,7 @@ permissions:
 
 jobs:
   build:
-    # Use Ubuntu 20.04 because doxygen 1.8.13 from Ubuntu 18.04 is broken.
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     steps:
     - uses: actions/checkout@d632683dd7b4114ad314bca15554477dd762a938 # v4.2.0