Force ubuntu-latest like on master

For some reason 22.04 is now randomly failing with old ghcs (that
should have been built on it??) with GLIBC and GLIBCXX versioning
errors. This doesn't show up on `master`, and this PR was failing
until I bumped it up to ubuntu-latest as well.

As with `master`, `validate-old-ghcs` still uses ubuntu-22.04
because they need `libtinfo6` which isn't available on 24.04.

Author: geekosaur

.github/workflows/validate.yml

@@ -53,7 +53,7 @@ jobs:
       matrix:
         sys:
           - { os: windows-latest, shell: "C:/msys64/usr/bin/bash.exe -e {0}" }
-          - { os: ubuntu-22.04, shell: bash }
+          - { os: ubuntu-latest, shell: bash }
           - { os: macos-latest, shell: bash }
         # If you remove something from here, then add it to the old-ghcs job.
         # Also a removed GHC from here means that we are actually dropping