testmap: Enable rhel-10-0 for c-machines

The "wild west" days are over, and RHEL 10 is nearing its beta release.
We need to properly test c-machines there as we release to it.

lib/testmap.py

@@ -136,14 +136,14 @@ def contexts(image: str, *scenarios: Iterable[str], repo: str | None = None) ->
             'rhel-8-10',
             'rhel-9-5',
             'rhel-9-6',
+            'rhel-10-0',
         ],
         'rhel-8': [
             'rhel-8-10',
         ],
         '_manual': [
             'centos-10',
             'fedora-rawhide',
-            'rhel-10-0',
         ],
     },
     'cockpit-project/cockpit-files': {