chore: require copyright assignment in PR template #1719

Job	Run time
Build wheels on macOS (x86_64)	8m 25s
Build wheels on Linux (x86_64)	24m 37s
Build wheels on macOS (arm64)	8m 46s
Build sdist and test extra dependencies	2m 11s
Build wheels on Linux (aarch64/manylinux)	15m 57s
Build wheels on Linux (i686)	19m 17s
Build wheels on Linux (aarch64/musllinux)	6m 18s
Build wheels for WebAssembly	6m 11s
Build with sanitizers for debugging purposes	2m 9s
Build wheels on Windows (Win32)	13m 4s
Build wheels on Windows (x64)	27m 9s
	2h 14m 4s

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