Fix raise_error warning

WARNING: Using `expect { }.not_to raise_error(SpecificErrorClass)` risks
false positives, since literally any other error would cause the
expectation to pass, including those raised by Ruby (e.g.
`NoMethodError`, `NameError` and `ArgumentError`), meaning the code you
are intending to test may not even get reached. Instead consider using
`expect { }.not_to raise_error` or `expect { }.to
raise_error(DifferentSpecificErrorClass)`.

spec/lib/gitlab/usage/metric_definition_spec.rb

@@ -44,7 +44,7 @@ RSpec.describe Gitlab::Usage::MetricDefinition do
   end
 
   it 'has all definitons valid' do
-    expect { described_class.definitions }.not_to raise_error(Gitlab::Usage::Metric::InvalidMetricError)
+    expect { described_class.definitions }.not_to raise_error
   end
 
   describe '#key' do