Remove support for Python 3.7 #368

Job	Run time
get-test-groups	3s
"python=3.8", group_spark_001	12m 53s
"python=3.8", group_notebooks_spark_001	12m 52s
"python=3.8", group_notebooks_spark_002	12m 52s
"python=3.8", group_gpu_001	12m 53s
"python=3.8", group_gpu_002	12m 54s
"python=3.8", group_notebooks_gpu_001	12m 54s
"python=3.8", group_notebooks_gpu_002	12m 58s
"python=3.8", group_cpu_001	12m 53s
"python=3.8", group_notebooks_cpu_001	12m 52s
"python=3.9", group_spark_001	12m 56s
"python=3.9", group_notebooks_spark_001	12m 52s
"python=3.9", group_notebooks_spark_002	12m 49s
"python=3.9", group_gpu_001	12m 48s
"python=3.9", group_gpu_002	12m 54s
"python=3.9", group_notebooks_gpu_001	12m 52s
"python=3.9", group_notebooks_gpu_002	12m 52s
"python=3.9", group_cpu_001	12m 53s
"python=3.9", group_notebooks_cpu_001	12m 35s
	3h 51m 35s

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