Update NewRelic::Agent::Tracer.in_transaction to identify category as a required kwarg

[tannalynn]

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Overview

When support for Ruby 2.0 was dropped in version 8.0.0 of the agent, the agent API methods were updated to use the required keyword argument feature built in to Ruby, rather than manually raising ArgumentError's. The API method NewRelic::Agent::Tracer.in_transaction removed the ArgumentError raised by the agent, but did not update the method arguments to identify category as a required keyword argument. resolves #1583

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[github-actions]

SimpleCov Report

	Coverage	Threshold
Line	93.28%	93%
Branch	84.18%	84%