ci/oss-fuzz: switch to Ubuntu 24.04

With
https://github.com/google/oss-fuzz/pull/14112 and
https://github.com/google/oss-fuzz/pull/14128,
we can now use Ubuntu 24.04. Let's bump the image version.

Note, the i386 build failure mentioned in the removed comment is related to
https://bugs.launchpad.net/ubuntu/+source/linux-signed-azure/+bug/2071445
https://github.com/actions/runner-images/issues/9977
and has been already fixed.

.github/workflows/cifuzz.yml

@@ -22,8 +22,7 @@ on:
       - main
 jobs:
   Fuzzing:
-    # FIXME: Figure out why 32-bit applications fail to run in docker on Ubuntu 24.04.
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     if: github.repository == 'systemd/systemd'
     concurrency:
       group: ${{ github.workflow }}-${{ matrix.sanitizer }}-${{ matrix.architecture }}-${{ github.ref }}