Add GitHub action infrastructure.

src/main.ts

@@ -0,0 +1,12 @@
+import * as core from '@actions/core'
+
+async function run(): Promise<void> {
+  try {
+    let graalVMHome
+    core.exportVariable('GRAALVM_HOME', graalVMHome)
+  } catch (error) {
+    if (error instanceof Error) core.setFailed(error.message)
+  }
+}
+
+run()