release: bump version to 3.1.9 (#124) #101

Job	Run time
test unit 3.1.x	4m 22s
test windows unit net6	7m 51s
test unit 9.0.x	4m 7s
test windows unit net5	8m 51s
test windows unit net7	7m 54s
test unit 7.0.x	4m 4s
test windows unit netcoreapp3.1	8m 17s
test windows unit net9	10m 15s
test unit 8.0.x	4m 47s
test unit 5.0.x	4m 36s
test windows unit net8	7m 27s
test unit 6.0.x	4m 5s
test windows unit net46	7m 2s
	1h 23m 38s

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