Work on build-tarball: Switch to Ubuntu 24.04, to avoid a gcc 11 warning during "make distcheck".

Author: bhaible

.github/workflows/many-platforms.yml

@@ -47,7 +47,7 @@ env:
 
 jobs:
   build-tarball:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     steps:
       # This is needed because we run a script stored in this repository.
       - uses: actions/checkout@v4