Added sql-server tests for dbt 1.3.0 to 1.8.0 #578

Job	Run time
integration (snowflake)	2m 16s
integration (bigquery)	2m 53s
integration (postgres)	1m 30s
single-run-different-versions (snowflake, 1_3_0)	1m 25s
single-run-different-versions (snowflake, 1_4_0)	1m 26s
single-run-different-versions (snowflake, 1_5_0)	1m 29s
single-run-different-versions (snowflake, 1_6_0)	1m 33s
single-run-different-versions (snowflake, 1_7_0)	1m 29s
single-run-different-versions (snowflake, 1_8_0)	1m 25s
single-run-different-versions (bigquery, 1_3_0)	2m 9s
single-run-different-versions (bigquery, 1_4_0)	2m 5s
single-run-different-versions (bigquery, 1_5_0)	2m 1s
single-run-different-versions (bigquery, 1_6_0)	2m 2s
single-run-different-versions (bigquery, 1_7_0)	1m 58s
single-run-different-versions (bigquery, 1_8_0)	1m 57s
single-run-different-versions (postgres, 1_3_0)	1m 3s
single-run-different-versions (postgres, 1_4_0)	1m 15s
single-run-different-versions (postgres, 1_5_0)	1m 21s
single-run-different-versions (postgres, 1_6_0)	1m 8s
single-run-different-versions (postgres, 1_7_0)	1m 15s
single-run-different-versions (postgres, 1_8_0)	1m 13s
single-run-different-versions (sqlserver, 1_3_0)	1m 50s
single-run-different-versions (sqlserver, 1_4_0)	2m 10s
single-run-different-versions (sqlserver, 1_5_0)	46s
single-run-different-versions (sqlserver, 1_6_0)	44s
single-run-different-versions (sqlserver, 1_7_0)	1m 41s
single-run-different-versions (sqlserver, 1_8_0)	1m 45s
	43m 49s

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