Use asArray utility to simplify OS filtering logic

Replaces separate string/array handling with asArray helper.

Author: cderv

tests/smoke/smoke-all.test.ts

@@ -12,6 +12,7 @@ import {
   setInitializer,
 } from "../../src/core/lib/yaml-validation/state.ts";
 import { os } from "../../src/deno_ral/platform.ts";
+import { asArray } from "../../src/core/array.ts";
 
 import { breakQuartoMd } from "../../src/core/lib/break-quarto-md.ts";
 import { parse } from "../../src/core/yaml.ts";
@@ -103,18 +104,8 @@ function skipTest(metadata: Record<string, any>): string | undefined {
 
   // Skip on specific OS if skip-on-os is set
   const skipOnOs = quartoMeta?.["skip-on-os"];
-  if (skipOnOs !== undefined) {
-    // Handle array of OSes
-    if (Array.isArray(skipOnOs)) {
-      if (skipOnOs.includes(os)) {
-        return `skip-on-os includes ${os}`;
-      }
-    }
-
-    // Handle single OS string
-    if (typeof skipOnOs === "string" && skipOnOs === os) {
-      return `skip-on-os is ${os}`;
-    }
+  if (skipOnOs !== undefined && asArray(skipOnOs).includes(os)) {
+    return `skip-on-os includes ${os}`;
   }
 
   return undefined;