Added sql-server tests for dbt 1.3.0 to 1.8.0 #580

Job	Run time
integration (snowflake)	2m 22s
integration (bigquery)	3m 8s
integration (postgres)	1m 27s
single-run-different-versions (snowflake, 1_3_0)	1m 29s
single-run-different-versions (snowflake, 1_4_0)	1m 43s
single-run-different-versions (snowflake, 1_5_0)	1m 38s
single-run-different-versions (snowflake, 1_6_0)	1m 34s
single-run-different-versions (snowflake, 1_7_0)	1m 41s
single-run-different-versions (snowflake, 1_8_0)	1m 30s
single-run-different-versions (bigquery, 1_3_0)	1m 51s
single-run-different-versions (bigquery, 1_4_0)	2m 5s
single-run-different-versions (bigquery, 1_5_0)	1m 50s
single-run-different-versions (bigquery, 1_6_0)	1m 56s
single-run-different-versions (bigquery, 1_7_0)	1m 53s
single-run-different-versions (bigquery, 1_8_0)	1m 55s
single-run-different-versions (postgres, 1_3_0)	1m 11s
single-run-different-versions (postgres, 1_4_0)	1m 22s
single-run-different-versions (postgres, 1_5_0)	1m 9s
single-run-different-versions (postgres, 1_6_0)	1m 9s
single-run-different-versions (postgres, 1_7_0)	1m 14s
single-run-different-versions (postgres, 1_8_0)	1m 11s
single-run-different-versions (sqlserver, 1_3_0)	2m 0s
single-run-different-versions (sqlserver, 1_4_0)	2m 15s
single-run-different-versions (sqlserver, 1_5_0)	44s
single-run-different-versions (sqlserver, 1_6_0)	43s
single-run-different-versions (sqlserver, 1_7_0)	1m 44s
single-run-different-versions (sqlserver, 1_8_0)	1m 52s
	44m 36s

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