Add riscv64gc to CI #1515

Job	Run time
Clippy	17s
Rustfmt	5s
Test (aarch64-apple-darwin, macos-latest, nightly)	2m 6s
Test (aarch64-unknown-linux-gnu, ubuntu-latest, nightly)	6m 45s
Test (aarch64-pc-windows-msvc, windows-latest, nightly, 1, 1)	1m 28s
Test (arm-unknown-linux-gnueabi, ubuntu-latest, nightly)	6m 48s
Test (arm-unknown-linux-gnueabihf, ubuntu-latest, nightly)	6m 33s
Test (i586-unknown-linux-gnu, ubuntu-latest, nightly)	4m 59s
Test (i686-unknown-linux-gnu, ubuntu-latest, nightly)	4m 51s
Test (powerpc-unknown-linux-gnu, ubuntu-latest, nightly)	6m 19s
Test (powerpc64-unknown-linux-gnu, ubuntu-latest, nightly)	5m 51s
Test (powerpc64le-unknown-linux-gnu, ubuntu-latest, nightly)	6m 5s
Test (riscv64gc-unknown-linux-gnu, ubuntu-latest, nightly)	1m 41s
Test (thumbv6m-none-eabi, ubuntu-latest, nightly)	4m 35s
Test (thumbv7em-none-eabi, ubuntu-latest, nightly)	4m 21s
Test (thumbv7em-none-eabihf, ubuntu-latest, nightly)	4m 33s
Test (thumbv7m-none-eabi, ubuntu-latest, nightly)	4m 20s
Test (wasm32-unknown-unknown, ubuntu-latest, nightly)	4m 53s
Test (x86_64-unknown-linux-gnu, ubuntu-latest, nightly)	4m 42s
Test (x86_64-apple-darwin, macos-13, nightly)	5m 10s
Test (i686-pc-windows-msvc, windows-latest, nightly, 1)	4m 18s
Test (x86_64-pc-windows-msvc, windows-latest, nightly, 1)	3m 56s
Test (i686-pc-windows-gnu, windows-latest, nightly-i686-gnu)	4m 48s
Test (x86_64-pc-windows-gnu, windows-latest, nightly-x86_64-gnu)	4m 44s
success	1s
	1h 44m 9s

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