Drop Python 3.6 support #1147

Job	Run time
Test frontend	49s
Lint	1m 17s
Test mcp-server on 3.8	13m 6s
Test mcp-server on 3.9	9m 58s
Test mcp-server on 3.10	10m 43s
Test mcp-client on 3.8	11m 19s
Test mcp-client on 3.9	14m 59s
Test mcp-client on 3.10	13m 45s
Test dashboard on 3.8	13m 15s
Test dashboard on 3.9	13m 37s
Test dashboard on 3.10	14m 54s
Test archivematica-common on 3.8	9m 33s
Test archivematica-common on 3.9	10m 27s
Test archivematica-common on 3.10	10m 57s
Test storage-service on 3.9	13m 27s
Test migrations on 3.9	12m 20s
	2h 54m 26s

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