igl | Add `pull_request_template.md` #1923

Job	Run time
Android (Ubuntu)	10m 16s
cmake-build (Windows - MSVC 2022, windows-latest, Debug, cl, cl, Visual Studio 17 2022, -DIGL_WIT...	8m 0s
cmake-build (Windows - MSVC 2022 (no OpenGL), windows-latest, Debug, cl, cl, Visual Studio 17 202...	6m 51s
cmake-build (Ubuntu - Clang, ubuntu-latest, Debug, clang, clang++, Unix Makefiles, -DIGL_WITH_TRA...	7m 34s
cmake-build (Ubuntu - GCC, ubuntu-latest, Debug, gcc, g++, Unix Makefiles, -DIGL_WITH_TRACY=ON -D...	5m 26s
cmake-build (macOS - Clang (Xcode), macos-latest, Debug, clang, clang++, Xcode, -DIGL_WITH_VULKAN...	51m 47s
cmake-build (macOS - Clang (Unix Makefiles), macos-latest, Debug, clang, clang++, Unix Makefiles,...	56m 36s
	2h 26m 30s

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