Change error on empty subjectAltNames #117

Job	Run time
Build docs & run doctests	29s
Verify dev env (ubuntu-latest)	22s
Run linters	4s
Type-check package	17s
Tests on 3.8	1m 17s
Verify dev env (windows-latest)	59s
Tests on 3.9	1m 14s
Verify dev env (macos-latest)	38s
Tests on 3.10	1m 0s
Tests on 3.11	1m 0s
Tests on 3.12	1m 8s
Tests on pypy-3.8	1m 13s
Tests on pypy-3.9	1m 20s
Combine & check coverage	15s
required-checks-pass	3s
	11m 19s

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