github: Update 'ubuntu-22.04' to 'ubuntu-latest' (#1022)

There was some inconsistency in the GitHub Workflow files on using
'ubuntu-latest' (which gets the latest Ubuntu version) or
'ubuntu-22.04'. To keep things consistent 'ubuntu-latest' is now used in
all cases. This also saves us updating workloads upon release of a new
Ubuntu version.

.github/workflows/daily-tests.yaml

@@ -304,7 +304,7 @@ jobs:
         # I.e., if we want to stop pull requests from being merged if the
         # daily tests are failing we can add this job as a required status
         # check.
-        runs-on: ubuntu-22.04
+        runs-on: ubuntu-latest
         needs:
             - unittests-fast-debug
             - testlib-long-tests