KVM: selftests: Explicitly include committed one-off assets in .gitignore

Add KVM selftests' one-off assets, e.g. the Makefile, to the .gitignore so
that they are explicitly included.  The justification for omitting the
one-offs was that including them wouldn't help prevent mistakes:

  Deliberately do not include the one-off assets, e.g. config, settings,
  .gitignore itself, etc as Git doesn't ignore files that are already in
  the repository.  Adding the one-off assets won't prevent mistakes where
  developers forget to --force add files that don't match the "allowed".

Turns out that's not the case, as W=1 will generate warnings, and the
amazing-as-always kernel test bot reports new warnings:

   tools/testing/selftests/kvm/.gitignore: warning: ignored by one of the .gitignore files
   tools/testing/selftests/kvm/Makefile: warning: ignored by one of the .gitignore files
>> tools/testing/selftests/kvm/Makefile.kvm: warning: ignored by one of the .gitignore files
   tools/testing/selftests/kvm/config: warning: ignored by one of the .gitignore files
   tools/testing/selftests/kvm/settings: warning: ignored by one of the .gitignore files

Fixes: 43e96957 ("KVM: selftests: Use pattern matching in .gitignore")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202408211818.85zIkDEK-lkp@intel.com
Link: https://lore.kernel.org/r/20240828215800.737042-1-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/.gitignore

@@ -5,3 +5,7 @@
 !*.h
 !*.S
 !*.sh
+!.gitignore
+!config
+!settings
+!Makefile