Use ubuntu-26.04 for Doctest and Cross build Linux

Author: vstinner

.github/workflows/build.yml

@@ -568,7 +568,7 @@ jobs:
 
   cross-build-linux:
     name: Cross build Linux
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     needs: build-context
     if: needs.build-context.outputs.run-ubuntu == 'true'

.github/workflows/reusable-docs.yml

@@ -95,7 +95,7 @@ jobs:
   # Run "doctest" on HEAD as new syntax doesn't exist in the latest stable release
   doctest:
     name: 'Doctest'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     steps:
     - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0