Add .idea to gitignore. #28

Job	Run time
build (linux, single, x86_64, template_debug, ubuntu-20.04)	7m 45s
build (windows, single, x86_32, template_debug, windows-latest)	10m 15s
build (windows, single, x86_64, template_debug, windows-latest)	10m 14s
build (macos, single, universal, template_debug, macos-latest)	7m 8s
build (android, single, arm64, template_debug, ubuntu-20.04)	6m 13s
build (android, single, arm32, template_debug, ubuntu-20.04)	7m 29s
build (android, single, x86_64, template_debug, ubuntu-20.04)	6m 16s
build (android, single, x86_32, template_debug, ubuntu-20.04)	7m 19s
build (ios, single, arm64, template_debug, macos-latest)	3m 47s
build (web, single, wasm32, template_debug, ubuntu-20.04)	14m 28s
build (linux, single, x86_64, template_release, ubuntu-20.04)	7m 52s
build (linux, double, x86_64, template_debug, ubuntu-20.04)	7m 51s
build (windows, double, x86_32, template_debug, windows-latest)	9m 11s
build (windows, double, x86_64, template_debug, windows-latest)	8m 46s
build (macos, double, universal, template_debug, macos-latest)	7m 30s
build (android, double, arm64, template_debug, ubuntu-20.04)	6m 18s
build (android, double, arm32, template_debug, ubuntu-20.04)	6m 6s
build (android, double, x86_64, template_debug, ubuntu-20.04)	7m 16s
build (android, double, x86_32, template_debug, ubuntu-20.04)	6m 59s
build (ios, double, arm64, template_debug, macos-latest)	3m 41s
build (web, double, wasm32, template_debug, ubuntu-20.04)	14m 31s
build (linux, double, x86_64, template_release, ubuntu-20.04)	7m 56s
merge	4s
	2h 54m 55s

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