Tests

Add test support for 3.15 #1291

Job	Run time
Build bloomberg-comdb2 from source	4m 45s
Build python-comdb2 source distribution	39s
Test suite (3.13)	46s
Test suite (3.12)	41s
Test suite (3.8)	50s
Test suite (3.9)	1m 11s
Test suite (3.10)	42s
Test suite (3.11)	47s
Test suite (3.14)	39s
Test suite (3.15-dev)	51s
	11m 51s

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