Backport datadog `span_type` change to 1.13.x #1974

Job	Run time
test (Gemfile, 3, 1)	1m 2s
legacy_test	2m 48s
test (gemfiles/rails_4.2.gemfile, 2.4, 1)	1m 38s
javascript_test	1m 16s
test (gemfiles/rails_5.2.gemfile, 2.7)	3m 2s
lint	1m 4s
test (gemfiles/rails_7.0.gemfile, 3)	1m 23s
mongodb_test (gemfiles/mongoid_6.gemfile)	1m 37s
test (gemfiles/rails_master.gemfile, 3)	2m 47s
postgres_test	2m 14s
mongodb_test (gemfiles/mongoid_7.gemfile)	1m 32s
system_tests	52s
	21m 15s

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