ktest.pl minconfig: Unset configs instead of just removing them

After a full run of a make_min_config test, I noticed there were a lot of
CONFIGs still enabled that really should not be. Looking at them, I
noticed they were all defined as "default y". The issue is that the test
simple removes the config and re-runs make oldconfig, which enables it
again because it is set to default 'y'. Instead, explicitly disable the
config with writing "# CONFIG_FOO is not set" to the file to keep it from
being set again.

With this change, one of my box's minconfigs went from 768 configs set,
down to 521 configs set.

Link: https://lkml.kernel.org/r/20221202115936.016fce23@gandalf.local.home

Cc: stable@vger.kernel.org
Fixes: 0a05c769 ("ktest: Added config_bisect test type")
Reviewed-by: John 'Warthog9' Hawley (VMware) <warthog9@eaglescrag.net>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

tools/testing/ktest/ktest.pl

@@ -3768,9 +3768,10 @@ sub test_this_config {
     # .config to make sure it is missing the config that
     # we had before
     my %configs = %min_configs;
-    delete $configs{$config};
+    $configs{$config} = "# $config is not set";
     make_new_config ((values %configs), (values %keep_configs));
     make_oldconfig;
+    delete $configs{$config};
     undef %configs;
     assign_configs \%configs, $output_config;