Add Python 3.13 support using `legacy-cgi` #101

Job	Run time
Validate coverage	30s
Build the documentation	25s
Lint the package	26s
Python: 3.8- on ubuntu-latest	23s
Python: 3.8- on windows-latest	1m 7s
Python: 3.8- on macos-latest	55s
Python: 3.9- on ubuntu-latest	27s
Python: 3.9- on windows-latest	1m 4s
Python: 3.9- on macos-latest	25s
Python: 3.10- on ubuntu-latest	24s
Python: 3.10- on windows-latest	1m 3s
Python: 3.10- on macos-latest	29s
Python: 3.11- on ubuntu-latest	25s
Python: 3.11- on windows-latest	1m 4s
Python: 3.11- on macos-latest	21s
Python: 3.12- on ubuntu-latest	28s
Python: 3.12- on windows-latest	1m 6s
Python: 3.12- on macos-latest	23s
Python: 3.13- on ubuntu-latest	36s
Python: 3.13- on windows-latest	1m 2s
Python: 3.13- on macos-latest	45s
Python: pypy-3.8- on ubuntu-latest	34s
Python: pypy-3.9- on ubuntu-latest	43s
Python: pypy-3.10- on ubuntu-latest	45s
Python: pypy-3.10- on windows-latest	34s
Python: pypy-3.10- on macos-latest	43s
	17m 7s

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