tests

Add MIX support #1748

Job	Run time
reuse	7s
windows	8m 5s
cpp-linter	1m 35s
test (ubuntu-latest, minimal, 5.15.*)	2m 52s
xmllint	14s
test (ubuntu-latest, full, 5.15.*)	44s
test (ubuntu-latest, full-debug, 5.15.*)	42s
test (macos-latest, minimal, 5.15.*)	4m 17s
test (macos-latest, full, 5.15.*)	6m 39s
test (macos-latest, full-debug, 5.15.*)	6m 23s
test (ubuntu-latest, full, 5.9.*)	40s
test (ubuntu-latest, minimal, 6.0.*)	1m 34s
test (ubuntu-latest, minimal, 6..)	3m 56s
test (macos-latest, minimal, 6..)	11m 56s
	49m 44s

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