Improve support for Mandrel distribution.

Fixes #48

src/main.ts

@@ -51,9 +51,13 @@ async function run(): Promise<void> {
           graalVMHome = await graalvm.setUpGraalVMJDKCE(javaVersion)
           break
         case c.DISTRIBUTION_MANDREL:
-          throw new Error(
-            `Mandrel requires the 'version' option (see https://github.com/graalvm/setup-graalvm/tree/main#options).`
-          )
+          if (graalvmVersion.startsWith(c.MANDREL_NAMESPACE)) {
+            graalVMHome = await setUpMandrel(graalvmVersion, javaVersion)
+          } else {
+            throw new Error(
+              `Mandrel requires the 'version' option (see https://github.com/graalvm/setup-graalvm/tree/main#options).`
+            )
+          }
         case '':
           if (javaVersion === c.VERSION_DEV) {
             core.info(