test: add missing --skip-confirmation to NPM 7 ng add test

This tests fails with
```
No terminal detected. '--skip-confirmation' can be used to bypass installation confirmation. Ensure package name is correct prior to '--skip-confirmation' option usage.
Command aborted.
```

(cherry picked from commit 9175811)

Author: alan-agius4

tests/legacy-cli/e2e/tests/misc/npm-7.ts

@@ -38,7 +38,10 @@ export default async function () {
     await npm('install', '--global', 'npm@7.4.0');
 
     // Ensure `ng add` shows npm warning
-    const { stderr: stderrAdd } = await ng('add', '@angular/localize');
+    // The below command will fail with the below due to incorrect peerDeps
+    const { message: stderrAdd } = await expectToFail(() =>
+      ng('add', '@angular/localize', '--skip-confirmation'),
+    );
     if (!stderrAdd.includes(warningText)) {
       throw new Error('ng add expected to show npm version warning.');
     }