Drop Python 3.6 support #1153

Job	Run time
Test frontend	46s
Lint	1m 17s
Test mcp-server on 3.8	10m 24s
Test mcp-server on 3.9	11m 43s
Test mcp-server on 3.10	10m 6s
Test mcp-client on 3.8	11m 3s
Test mcp-client on 3.9	13m 11s
Test mcp-client on 3.10	11m 38s
Test dashboard on 3.8	12m 37s
Test dashboard on 3.9	10m 58s
Test dashboard on 3.10	15m 0s
Test archivematica-common on 3.8	9m 34s
Test archivematica-common on 3.9	9m 40s
Test archivematica-common on 3.10	10m 22s
Test storage-service on 3.9	13m 57s
Test migrations on 3.9	10m 13s
	2h 42m 29s

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