Attempt to trick Ruby 3.1

The error message seems mangled on GitHub action with some versions of
Ruby.  Not sure about the real root cause, but matching unitf a Regexp
seems to help here.

spec/unit/mcollective/pluginpackager_spec.rb

@@ -21,7 +21,7 @@ module MCollective
       it "should do something else" do
         expect{
           PluginPackager["Bar"]
-        }.to raise_error(NameError, 'uninitialized constant MCollective::PluginPackager::Bar')
+        }.to raise_error(NameError, /uninitialized constant MCollective::PluginPackager::Bar/)
       end
     end