Support using httpbin without flasgger #17

Job	Run time
unit-tests (3.7, ubuntu-22.04)	59s
unit-tests (3.7, macOS-latest)	3m 7s
unit-tests (3.7, windows-latest)	4m 10s
unit-tests (3.8, ubuntu-22.04)	57s
unit-tests (3.8, macOS-latest)	3m 17s
unit-tests (3.8, windows-latest)	3m 48s
unit-tests (3.9, ubuntu-22.04)	57s
unit-tests (3.9, macOS-latest)	2m 18s
unit-tests (3.9, windows-latest)	4m 3s
unit-tests (3.10, ubuntu-22.04)	48s
unit-tests (3.10, macOS-latest)	3m 43s
unit-tests (3.10, windows-latest)	3m 41s
unit-tests (3.11, ubuntu-22.04)	1m 0s
unit-tests (3.11, macOS-latest)	2m 40s
unit-tests (3.11, windows-latest)	3m 44s
unit-tests (3.12-dev, ubuntu-22.04)	1m 2s
unit-tests (3.12-dev, macOS-latest)	3m 26s
unit-tests (3.12-dev, windows-latest)	3m 49s
unit-tests (pypy-3.8, ubuntu-22.04)	3m 21s
unit-tests (pypy-3.8, macOS-latest)	8m 52s
unit-tests (pypy-3.8, windows-latest)	6m 6s
unit-tests (pypy-3.9, ubuntu-22.04)	3m 24s
unit-tests (pypy-3.9, macOS-latest)	6m 30s
unit-tests (pypy-3.9, windows-latest)	6m 57s
unit-tests (pypy-3.10, ubuntu-22.04)	3m 13s
unit-tests (pypy-3.10, macOS-latest)	5m 18s
unit-tests (pypy-3.10, windows-latest)	6m 46s
publish-docker-image	52s
	1h 38m 48s

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