test(commonjs): document expected stub throw; align snapshots

Author: CharlieHelps

packages/commonjs/test/fixtures/function/module-side-effects-external-node-builtin-wrapped-stub/main.js

@@ -10,6 +10,11 @@ function unused() {
 
 try {
   unused();
-} catch {}
+} catch (_err) {
+  // Expected: in this fixture we configure `externalBuiltinsRequire: 'stub'`,
+  // so calling the proxy's `__require()` throws. We swallow the error so the
+  // test can assert on the generated code (no `node:module` import) without
+  // failing at runtime.
+}
 
 module.exports = 1;

packages/commonjs/test/snapshots/function.js.md

@@ -6762,7 +6762,12 @@ Generated by [AVA](https://avajs.dev).
       ␊
       	try {␊
       	  unused();␊
-      	} catch {}␊
+      	} catch (_err) {␊
+      	  // Expected: in this fixture we configure \`externalBuiltinsRequire: 'stub'\`,␊
+      	  // so calling the proxy's \`__require()\` throws. We swallow the error so the␊
+      	  // test can assert on the generated code (no \`node:module\` import) without␊
+      	  // failing at runtime.␊
+      	}␊
       ␊
       	main$1 = 1;␊
       	return main$1;␊