Adding support for RISC-V arch

On behalf of https://github.com/helm/helm/issues/11341

CC @lazyparser @carlosedp

Signed-off-by: gghjgj <yantitarenko5@gmail.com>

pkg/plugin/plugin_test.go

@@ -92,6 +92,7 @@ func TestPlatformPrepareCommand(t *testing.T) {
 				{OperatingSystem: "linux", Architecture: "ppc64le", Command: "echo -n linux-ppc64le"},
 				{OperatingSystem: "linux", Architecture: "s390x", Command: "echo -n linux-s390x"},
 				{OperatingSystem: "windows", Architecture: "amd64", Command: "echo -n win-64"},
+				{OperatingSystem: "linux", Architecture: "riscv64", Command: "echo -n linux-riscv64"},
 			},
 		},
 	}
@@ -108,6 +109,9 @@ func TestPlatformPrepareCommand(t *testing.T) {
 		osStrCmp = "linux-ppc64le"
 	} else if os == "linux" && arch == "s390x" {
 		osStrCmp = "linux-s390x"
+	} 
+	else if os == "linux" && arch == "riscv64" {
+		osStrCmp = "linux-riscv64"
 	} else if os == "windows" && arch == "amd64" {
 		osStrCmp = "win-64"
 	} else {
@@ -126,6 +130,7 @@ func TestPartialPlatformPrepareCommand(t *testing.T) {
 			Command: "echo -n os-arch",
 			PlatformCommand: []PlatformCommand{
 				{OperatingSystem: "linux", Architecture: "i386", Command: "echo -n linux-i386"},
+				{OperatingSystem: "linux", Architecture: "riscv64", Command: "echo -n linux-riscv64"},
 				{OperatingSystem: "windows", Architecture: "amd64", Command: "echo -n win-64"},
 			},
 		},