Don't build all wheels all the time #13

Job	Run time
Build ijson and run unit tests (ubuntu-20.04, 3.7)	23s
Build ijson and run unit tests (ubuntu-20.04, 3.8)	16s
Build ijson and run unit tests (ubuntu-20.04, 3.9)	18s
Build ijson and run unit tests (ubuntu-20.04, 3.10)	26s
Build ijson and run unit tests (ubuntu-20.04, 3.11)	20s
Build ijson and run unit tests (ubuntu-20.04, 3.12)	18s
Build ijson and run unit tests (windows-2019, 3.7)	1m 23s
Build ijson and run unit tests (windows-2019, 3.8)	53s
Build ijson and run unit tests (windows-2019, 3.9)	38s
Build ijson and run unit tests (windows-2019, 3.10)	37s
Build ijson and run unit tests (windows-2019, 3.11)	1m 9s
Build ijson and run unit tests (windows-2019, 3.12)	1m 19s
Build ijson and run unit tests (macos-12, 3.7)	44s
Build ijson and run unit tests (macos-12, 3.8)	29s
Build ijson and run unit tests (macos-12, 3.9)	25s
Build ijson and run unit tests (macos-12, 3.10)	43s
Build ijson and run unit tests (macos-12, 3.11)	22s
Build ijson and run unit tests (macos-12, 3.12)	58s
Build ijson and run unit tests (ubuntu-20.04, pypy3.9)	32s
Build ijson and run unit tests (ubuntu-20.04, pypy3.10)	30s
	12m 43s

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