Add Python 3.13 support using `legacy-cgi` #115

Job	Run time
Build the documentation	27s
Validate coverage	33s
Lint the package	24s
Python: 3.8 on ubuntu-latest	31s
Python: 3.8 on windows-latest	1m 38s
Python: 3.8 on macos-latest	48s
Python: 3.9 on ubuntu-latest	25s
Python: 3.9 on windows-latest	1m 28s
Python: 3.9 on macos-latest	26s
Python: 3.10 on ubuntu-latest	25s
Python: 3.10 on windows-latest	1m 13s
Python: 3.10 on macos-latest	22s
Python: 3.11 on ubuntu-latest	29s
Python: 3.11 on windows-latest	1m 22s
Python: 3.11 on macos-latest	31s
Python: 3.12 on ubuntu-latest	28s
Python: 3.12 on windows-latest	1m 26s
Python: 3.12 on macos-latest	24s
Python: 3.13 on ubuntu-latest	36s
Python: 3.13 on windows-latest	1m 51s
Python: 3.13 on macos-latest	22s
Python: pypy-3.9 on ubuntu-latest	43s
Python: pypy-3.10 on ubuntu-latest	43s
Python: pypy-3.10 on windows-latest	2m 5s
Python: pypy-3.10 on macos-latest	41s
	20m 21s

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