Drop Python 3.6 support #1152

Job	Run time
Test frontend	49s
Lint	1m 30s
Test mcp-server on 3.8	5m 23s
Test mcp-server on 3.9	5m 22s
Test mcp-server on 3.10	5m 18s
Test mcp-client on 3.8	8m 8s
Test mcp-client on 3.9	5m 54s
Test mcp-client on 3.10	6m 25s
Test dashboard on 3.8	5m 53s
Test dashboard on 3.9	7m 5s
Test dashboard on 3.10	6m 4s
Test archivematica-common on 3.8	5m 8s
Test archivematica-common on 3.9	6m 45s
Test archivematica-common on 3.10	6m 50s
Test storage-service on 3.9	6m 38s
Test migrations on 3.9	5m 13s
	1h 28m 25s

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