Improve for matrix

Co-authored-by: Andrew Eisenberg <aeisenberg@github.com>

src/actions-util.ts

@@ -887,7 +887,7 @@ export async function uploadDebugArtifacts(
   }
   let suffix = "";
   const matrix = getRequiredInput("matrix");
-  if (matrix !== undefined && matrix !== "null") {
+  if (matrix) {
     for (const entry of Object.entries(JSON.parse(matrix)).sort())
       suffix += `-${entry[1]}`;
   }