Remove support for Python 3.7 #362

Job	Run time
get-test-groups	4s
"python=3.8", group_spark_001	27m 58s
"python=3.8", group_notebooks_spark_001	28m 14s
"python=3.8", group_notebooks_spark_002	28m 13s
"python=3.8", group_gpu_001	28m 14s
"python=3.8", group_gpu_002	28m 21s
"python=3.8", group_notebooks_gpu_001	28m 15s
"python=3.8", group_notebooks_gpu_002	28m 13s
"python=3.8", group_cpu_001	28m 14s
"python=3.8", group_notebooks_cpu_001	28m 14s
"python=3.9", group_spark_001	20m 44s
"python=3.9", group_notebooks_spark_001	24m 57s
"python=3.9", group_notebooks_spark_002	28m 14s
"python=3.9", group_gpu_001	28m 12s
"python=3.9", group_gpu_002	28m 16s
"python=3.9", group_notebooks_gpu_001	28m 12s
"python=3.9", group_notebooks_gpu_002	28m 15s
"python=3.9", group_cpu_001	28m 16s
"python=3.9", group_notebooks_cpu_001	27m 44s
	8h 16m 50s

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