Switch JAVA_HOME to 21 for JRuby

JRuby 10 requires Java 21. Since the previous default was 17 and
all JRuby releases should work fine on 21, we do this for all
JRuby installs.

Implements #718

Author: headius

common.js

@@ -403,3 +403,7 @@ export function setupPath(newPathEntries) {
   core.addPath(newPath.join(path.delimiter))
   return msys2Type
 }
+
+export function setupJavaHome() {
+  core.exportVariable("JAVA_HOME", process.env[`JAVA_HOME_21_${os.arch().toUpperCase()}`]);
+}

ruby-builder.js

@@ -49,6 +49,10 @@ export async function install(platform, engine, version) {
   // Set the PATH now, so the MSYS2 'tar' is in Path on Windows
   common.setupPath([path.join(rubyPrefix, 'bin')])
 
+  if (engine == "jruby") {
+    common.setupJavaHome();
+  }
+
   if (!inToolCache) {
     await io.mkdirP(rubyPrefix)
     await downloadAndExtract(platform, engine, version, rubyPrefix)