ci: add riscv64 to release build matrix (#7337)

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Signed-off-by: Bruno Verachten <gounthar@gmail.com>

install/install.sh

@@ -18,7 +18,8 @@ SUPPORTED_TARGETS="x86_64-unknown-linux-gnu x86_64-unknown-linux-musl \
                   arm-unknown-linux-musleabihf x86_64-apple-darwin \
                   aarch64-apple-darwin x86_64-pc-windows-msvc \
                   i686-pc-windows-msvc aarch64-pc-windows-msvc \
-                  x86_64-unknown-freebsd"
+                  x86_64-unknown-freebsd \
+                  riscv64gc-unknown-linux-musl"
 
 info() {
 	printf '%s\n' "${BOLD}${GREY}>${NO_COLOR} $*"
@@ -242,6 +243,7 @@ detect_arch() {
 	amd64) arch="x86_64" ;;
 	armv*) arch="arm" ;;
 	arm64) arch="aarch64" ;;
+	riscv64) arch="riscv64gc" ;;
 	esac
 
 	# `uname -m` in some cases mis-reports 32-bit OS as 64-bit, so double check