Fix license_trial instrumented metric

What does this MR do and why?

Use trial? as a license attribute for trial LicenseMetric license_trial

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How to set up and validate locally

Make sure you have a license for the environment where this is tested

# When using usgae_data.rb

Gitlab::UsageData.license_usage_data[:license_trial]
Gitlab::UsageData.license_usage_data[:license_id]

# When using  instrumentation classes only

Gitlab::UsageDataMetrics.uncached_data[:license_trial] 
Gitlab::UsageDataMetrics.uncached_data[:license_id] 

Both values should equal License.current.trial? License.current.license_id

MR acceptance checklist

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