test: avoid flaky debugger restart waits

Use command('restart') instead of stepCommand('restart') in two tests.

This avoids timing out while waiting for BREAK_MESSAGE on restart.
Keep assertions intact while using less fragile synchronization.

Refs: #61762

Author: inoway46

test/parallel/test-debugger-restart-message.js

@@ -25,7 +25,11 @@ const startCLI = require('../common/debugger');
       assert.strictEqual(cli.output.match(listeningRegExp).length, 1);
 
       for (let i = 0; i < RESTARTS; i++) {
-        await cli.stepCommand('restart');
+        // For `restart`, sync on attach/prompt instead of BREAK_MESSAGE to avoid flaky races.
+        // https://github.com/nodejs/node/issues/61762
+        await cli.command('restart');
+        await cli.waitFor(/Debugger attached\./);
+        await cli.waitForPrompt();
         assert.strictEqual(cli.output.match(listeningRegExp).length, 1);
       }
     } finally {

test/parallel/test-debugger-run-after-quit-restart.js

@@ -57,7 +57,7 @@ const path = require('path');
         { filename: script, line: 2 },
       );
     })
-    .then(() => cli.stepCommand('restart'))
+    .then(() => cli.command('restart'))
     .then(() => cli.waitForInitialBreak())
     .then(() => {
       assert.deepStrictEqual(